A person who lacks the means, within himself, to live a good and happy life will find any period of his existence wearisome. But rely for life’s blessings on your own resources, and you will not take a gloomy view of any of the inevitable consequences of nature’s laws. Everyone hopes to attain an advanced age; yet when it comes they all complain! So foolishly inconsistent and perverse can people be.

[Quibus enim nihil est in ipsis opis ad bene beateque vivendum, eis omnis aetas gravis est; qui autem omnia bona a se ipsi petunt, eis nihil malum potest videri quod naturae necessitas adferat. Quo in genere est in primis senectus, quam ut adipiscantur omnes optant, eandem accusant adeptam; tanta est stultitiae inconstantia atque perversitas.]

Marcus Tullius Cicero (106-43 BC) Roman orator, statesman, philosopher

De Senectute [Cato Maior; On Old Age], ch. 2 / sec. 4 (2.4) [Cato] (44 BC) [tr. Grant (1960, 1971 ed.)]
    (Source)

(Source (Latin)). Alternate translations:

For eche of thies ages which men name Childhode, adolescence, yongth, virilite, manhode & olde age semyn to be hevy & noxous to men the which in them silf have nothyng that may help & socoure them to lyve goodly & blessidly as bee, the which excercisen sciences & vertues & good werkis, but as to suche men which sechyn & fyndyn in themsilf alle the goods & thyngis which belongyn wele & blessidly for to lyve, ther is nothyng that comyth to them in age by the defaute of nature that may seme unto them evyll nor noxous. It is certayne that olde age is suche that it serchith & fyndyth in it self all the goodnesses whch longen to live wel & blyssidly, and yet is olde age such that alle men desyre to come untyll hit, And never the lesse the mutablenes & evyl dysposicion of men it is so grete in oure dayes that they blamyn olde age whan they be come therto by cause that then they may not use delectacions.
[tr. Worcester/Worcester/Scrope (1481)]

For they that have no power, pith of wit, help, way nor virtue in themselves to conduct and bring them to a good and blessed life, unto such as these be, all their age is cumbersome and unpleasant. But unto such as lead their lives virtuously, measuring all their actions by the square of reason, and have their minds with all good gifts of grace beautified and garnished, there is nothing thought nor deemed evil that cometh by necessity of nature. Of the which sort old age is principally to be considered, unto which all men wish to arrive, and yet when they have their desire, they accuse it as painful, sickly, unpleasant and tedious, such is the brainless unconstancy, foolish sottage, and perverse overthwartness of wayward people.
[tr. Newton (1569)]

For that age is only grievous to those that have no taste of wisdome and learning in themselves to make them live happily: but to them which see all perfection and consolation from their own experience, nothing can seem heavy which the necessity of nature bringeth: of which sort old age is chief, which all desire to obtain, and blame being obtained; such is their unconstancy, foolishnesse and perversity.
[tr. Austin (1648)]

For to those who have nothing within themselves capable of making Life happy, and satisfactory, no wonder if every Stage of it should prove irksome, and vexatious: but, to those who derive all their satisfaction from an easy mind, nothing can seem grievous and tormenting, that proceeds from the irreversible Laws of Nature; which certainly is the case of Old Age,, whereunto though 'tis the earnest desire of all men to arrive, yet such is their unaccountable folly, and perverseness, that they are never more uneasy than when they have arrived at it.
[tr. Hemming (1716)]

All Ages are grievous to those who have not in themselves the Means of living Holy and Happy; but those who expect all Happiness from their own Virtues, don't look up on the Decay of Nature as a Hardship, whereof Old Age is the chiefest, and which all desire to attain to; but is no sooner tasted than declaim'd against. Such are the Effects of Inconstancy, Folly, and the Want of Wisdom.
[tr. J. D. (1744)]

For know this, that those who have no Aid or Support within themselves, to render their Lives easy, will find every State irksome: While such as are convinced, they must owe their Happiness to themselves, and that if they cannot find it in their own Breasts, they will never meet with it from abroad; will never consider any thing as an Evil, that is but a necessary Effect of the established Order of Nature; which Old Age most undoubtedly is. 'Tis certainly strange, that while all Men hope they may live to attain it, any should find Fault with it, when it comes their Share. Yet such is the Levity, Folly, and Perverseness of Mankind, that we see there is nothing more common.
[tr. Logan (1744)]

Those indeed who have no internal resource of happiness, will find themselves uneasy in every stage of human life: but to him who is accustomed to derive all his felicity from within himself, no state will appear as a real evil into which he is conducted by the common and regular course of nature. Now this is peculiarly the case with respect to old age : yet such is the inconsistency of human folly, that the very period which at a distance is every man's warmest wish to attain, no sooner arrives than it is equally the object of his lamentations.
[tr. Melmoth (1773)]

For to those that have nought of resource in themselves for living well and happily, every stage of life is burthensome; while to those that seek all their goods from themselves, nothing can seem an evil, which the law of Nature may bring them. In which class foremost stands old age, which all desire to attain, but arraign the same when attained; so great is the inconsistency and perverseness of folly.
[Cornish Bros. ed. (1847)]

For to those who have no resource in themselves for living well and happily, every age is burdensome; but to those who seek all good things from themselves, nothing can appear evil which the necessity of nature entails; in which class particularly is old age, which all men wish to attain, and yet they complain of it when they have attained it; so great is the inconsistency and waywardness of folly.
[tr. Edmonds (1874)]

For those who have in themselves no resources for a good and happy life, every period of life is burdensome; but to those who seek all goods from within, nothing which comes in the course of nature can seem evil. Under this head a place especially belongs to old age, which all desire to attain, yet find fault with it when they have reached it. Such is the inconsistency and perverseness of human folly.
[tr. Peabody (1884)]

But those who look for all happiness from within can never think anything bad which nature makes inevitable. In that category before anything else comes old age, to which all wish to attain, and at which all grumble when attained. Such is Folly's inconsistency and unreasonableness!
[tr. Shuckburgh (1895)]

Of course
To those who've no resources in themselves
For a good and happy life, why, every age
Is hard to bear: but those who have within
All that is needful for a life well-spent,
Can never find misfortune in the lot
That nature's laws impose. And one such lot
Is that old age must come to each and all,
Old age so fondly hoped for, when it comes,
So Oft found to be irksome. Such, alas!
Is Folly's want of reason and resolve.
[tr. Allison (1916)]

For to those who have not the means within themselves of a virtuous and happy life every age is burdensome; and, on the other hand, to those who seek all good from themselves nothing can seem evil that the laws of nature inevitably impose. To this class old age especially belongs, which all men wish to attain and yet reproach when attained; such is the inconsistency and perversity of Folly!
[tr. Falconer (1923)]

People, you see, who have no inner resources for living the good and happy life, find every age a burden. But men who seek all good from within themselves are simply unable to view as evil anything that comes about through nature’s law. Now old age, as much as anything else in this world, is such a thing. All men hope and pray to attain it; once they have attained it, they start finding fault with it.
[tr. Copley (1967)]

Some people just do not possess the optimism that would allow them to live contentedly under any circumstances: for them every stage of life is a burden. But if only they expected nothing but good for themselves, nothing that the natural passage of time brought them could seem bad. This is especially true of old age. Everybody wants to live for a long time, but when they have attained their goal, they grumble. It makes no sense -- but that’s what life is: perverse and inconsistent.
[tr. Cobbold (2012)]

Someone who doesn't have much in the way of inner resources will find all stages of life irksome, but someone whose character is in order will accept what nature brings and not complain about something perfectly natural, calling it evil. There is much nonsense bandied about old age, something which everyone wishes to reach, but which most complain about once they get there. That seems more than slightly inconsistent and perverse, doesn't it?
[tr. Gerberding (2014)]

They find every age oppressive, of course,
Who in their inner selves have no resource
To live an easy life in happiness,
But they who in themselves only find
Their own contentment and peace of mind
See no harm in nature’s due process
Whose termination inevitably
May lead to that state of senility
To which they keenly lay claim,
But once attained rather foolishly,
With malice and incongruity,
Promptly find reasons to blame.
[tr. Bozzi (2015)]

Those who lack within themselves the means for living a blessed and happy life will find any age painful. But for those who seek good things within themselves, nothing imposed on them by nature will seem troublesome. Growing older is a prime example of this. Everyone hopes to reach old age, but when it comes, most of us complain about it. People can be so foolish and inconsistent.
[tr. Freeman (2016)]

Every age is burdensome to those who have no means of living well and happily. But to those who seek all good from themselves, nothing which the necessity of nature offers can appear bad. Old age is a prime example of this sort of thing -- everyone wishes to attain it, but they always complain about it once it is attained. Such is the inconstancy and perversity of stupidity.
[tr. Robinson [@sentantiq] (2017)]