Gravity is the shield of fools.
[tr. Clark (2012), # 1637]

Solemnity is the shield of idiots.
[E.g.]

Mrs. Darling came to the window, for at present she was keeping a sharp eye on Wendy. She told Peter that she had adopted all the other boys, and would like to adopt him also.
“Would you send me to school?” he inquired craftily.
“Yes.”
“And then to an office?”
“I suppose so.”
“Soon I should be a man?”
“Very soon.”
“I don’t want to go to school and learn solemn things,” he told her passionately. “I don’t want to be a man. O Wendy’s mother, if I was to wake up and feel there was a beard!”
“Peter,” said Wendy the comforter, “I should love you in a beard;” and Mrs. Darling stretched out her arms to him, but he repulsed her.
“Keep back, lady, no one is going to catch me and make me a man.”

What have you to say against laughing? Can we not while laughing be very serious? Laughing keeps us more rational than sadness caused by vexation.
[Source (1884)]

The cours and the weye of age is certeyne and determyned by nature, whiche hathe onely awey which is symple & is nothyng different more in the one than in the othir. But each go by that symple and determyned wey aftir the degrees in their cours from the one age in to that other. And yet nature had given to every part of age his owne propre season and tyme, and hir pertynent cours of usage in kynde. That is to witt, that sekenesse and maladye is appropryd to the age of puerice in childhode, & cruelte is appropryd to the age of yongth, worshipfulnesse and sadnesse of maners be appropryd to the age of virilite whiche is the fyfthe age. Moderaunce and temperaunce be appropryd to olde age. Eueriche oweth to have sumwhat naturelly and appropryd unto that whiche may be gadird in his tyme.
[tr. Worcester/Worcester/Scrope (1481), Part 3]

The race and course of age is certain; and there is but one way of nature and the same simple; and to every part of a man's life and age are given his convenient times and proper tempestivities. For even as weakness and infirmity is incident to young children, lustiness and bravery to young men, and gravity when they come to ripe years; so, likewise the maturity or ripeness of old age have a certain special gift given and attributed to it by nature, which ought not to be neglected, but to be taken in his own time and season when it cometh.
[tr. Newton (1569)]

There is but one course of age, and one way of nature, and the same simple, and to every part of age its own timelines is given; for as infirmity belongs to child-hood, fiercenesse to youth, and gravity to age, so the true ripenesse of age hath a certaine natural gravity in it, which ought to be used in it own time.
[tr. Austin (1648)]

Simple, and certain Nature's wayes appear,
As she sets forth the seasons of the year.
So in all parts of life we find her truth,
Weakness to childhood, rashness to our youth:
To elder years to be discreet and grave,
Then to old age maturity she gave.
[tr. Denham (1669)]

Every Age has something in it, peculiar to it self: as Weakness to our Infancy, an unguided Warmth to Youth, Seriousness to Manhood, and a certain Maturity of Judgment to Old Age, which we may expect to reap the Fruits of, when advanced to it.
[tr. Hemming (1716)]

Life has a sure Course, and Nature but one Way, that that too simple and plain. And to every Part of Man's Age a peculiar Propriety of Temper is given: Thus Weakness in Children, a Boldness in Youth, and a Gravity in Manhood appears; and a full Ripeness of Years has always something which seems natural to it, and which ought to be made use of at a proper Time.
[tr. J. D. (1744)]

The Stages of Life are fixed; Nature is the same in all, and goes on in a plain and steady Course: Every Part of Life, like the Year, has its peculiar Season: As Children are by Nature weak, Youth is rash and bold; staid Manhood more solid and grave; and so Old-Age in its Maturity, has something natural to itself, that ought particularly to recommend it.
[tr. Logan (1750)]

Nature conducts us, by a regular and insensible progression through the different seasons of human life; to each of which she has annexed its proper and distinguishing characteristic. As imbecility is the attribute of infancy, ardour of youth, and gravity of manhood; so declining age has its essential properties, which gradually disclose themselves as years increase.
[tr. Melmoth (1773)]

The course of life is fixed, and the path of nature is one, and that simple. And its own proper seasonableness has been given to each division of life; so that both the feebleness of boys and the proud spirit of young men, and the gravity of a now settle period of life, and the maturity of old age, has something natural to it, which ought to be gathered in its own season.
[Cornish Bros. ed. (1847)]

There is a definite career in life, and one way of nature, and that a simple one; and to every part ot life its own peculiar period has been assigned: so that both the feebleness of boys, and the high spirit of young men, and the steadiness of now fixed manhood, and the maturity of old age, have something natural, which ought to be enjoyed in their own time.
[tr. Edmonds (1874)]

Life has its fixed course, and nature one unvarying way; each age has assigned to it what best suits it, so that the fickleness of boyhood, the sanguine temper of youth, the soberness of riper years, and the maturity of old age, equally have something in harmony with nature, which ought to be made availing in its season.
[tr. Peabody (1884)]

The course of life is fixed, and nature admits of its being run but in one way, and only once; and to each part of our life there is something specially seasonable; so that the feebleness of children, as well as the high spirit of youth, the soberness of maturer years, and the ripe wisdom of old age -- all have a certain natural advantage which should be secured in its proper season.
[tr. Shuckburgh (1895)]

One only way
Nature pursues, and that a simple one:
To each is given what is fit for him.
The boy is weak: youth is more full of fire:
Increasing years have more of soberness:
And as in age there is a ripeness too.
Each should be garnered at its proper time,
And made the most of.
[tr. Allison (1916)]

Life's race-course is fixed; Nature has only a single path and that path is run but once, and to each stage of existence has been allotted its own appropriate quality; so that the weakness of childhood, the impetuosity of youth, the seriousness of middle life, the maturity of old age -- each bears some of Nature's fruit, which must be garnered in its own season.
[tr. Falconer (1923)]

The course of life is clear to see; nature has only one path, and it has no turnings. Each season of life has an advantage peculiarly its own; the innocence of children, the hot blood of youth, the gravity of the prime of life, and the mellowness of age all possess advantages that are theirs by nature, and that should be garnered each at its proper time.
[tr. Copley (1967)]

Life and nature have but one direction
Easy to take, without correction.
Each of life’s rite of passage dates
Has its own distinguishing traits:
A child’s weakness
A youth’s boldness
An adult’s authority
An old man’s maturity
And each with a certain natural zest
To be reaped when it’s time for its harvest.
[tr. Bozzi (2015)]

The course of life cannot change. Nature has but a single path and you travel it only once. Each stage of life has its own appropriate qualities -- weakness in childhood, boldness in youth, seriousness in middle age, and maturity in old age. These are fruits that must be harvested in due season.
[tr. Freeman (2016)]

Few of those things that occasion trouble, are to be minded: else we shall torment our selves much in vain. It's to act the clean contrary way, to lay that to heart, which we should throw behind our backs. Many things that were of some consequence, have signified nothing at all, because men troubled not themselves about them; and others which signified nothing, have become matters of importance, because of the value that was put upon them.
[Flesher ed. (1685)]

Troublesome things must not be taken too seriously if they can be avoided. It is preposterous to take to heart that which you should throw over your shoulders. Much that would be something has become nothing by being left alone and what was nothing has become of consequence by being made much of.
[tr. Jacobs (1892)]

To convert petty annoyances into matters of importance, is to become seriously involved in nothing. It is to miss the point, to carry on the chest what has been cast from the shoulders. Many things which were something, by being left alone became nothing; and others which were nothing, became much because messed into.
[tr. Fischer (1937)]

For truely it is to bee noted, that Childrens playes are not sports, and should be deemed as their most serious actions.
[tr. Florio (1603), ch. 22]

As it must be noted, that the plays of children are not in jest, but must be judged of as their most serious actions.
[tr. Cotton (1686)]

Indeed, it is to be noted, that the plays of children are not performed in play, but are to be judged in them as their most serious actions.
[tr. Cotton/Hazlitt (1877), ch. 22]

We must take note that the games of children are not games in their eyes; and we must regard these as their most serious actions.
[E.g. (1884)]

Indeed, it should be noted that the games of children are not games, and must be judged as their most serious acts.
[tr. Ives (1925), ch. 23]

Indeed it must be noted that children’s games are not games, and must be judged in children like their more serious actions.
[tr. Frame (1943), ch. 23]

Man is born to live, not to prepare for life. Life itself, the phenomenon of life, the gift of life, is so breath-takingly serious! So why substitute this childish harlequinade of immature fantasies, these schoolboy escapades?
[tr. Hayward & Harari (1958), US ed.]

Man is born to live, not to prepare for life. And life itself, the phenomenon of life, the gift of life, is so thrillingly serious! Why then substitute for it a childish harlequinade of immature inventions, these escapes of Chekhovian schoolboys to America?
[tr. Pevear & Volokhonsky (2010)]