Using maxims is appropriate for those who are older in age when uttered about things for which they have some experience. Using maxims before one is this age lacks propriety as does story-telling: to speak about what one has no experience in is foolish and uneducated. A sufficient sign of this is that bumpkins especially tend to make up maxims and they easily show them off.

[ἁρμόττει δὲ γνωμολογεῖν ἡλικίᾳ μὲν πρεσβυτέροις, περὶ δὲ τούτων ὧν ἔμπειρός τις ἐστί, ὡς τὸ μὲν μὴ τηλικοῦτον ὄντα γνωμολογεῖν ἀπρεπὲς ὥσπερ καὶ τὸ μυθολογεῖν, περὶ δ᾿ ὧν ἄπειρος, ἠλίθιον καὶ ἀπαίδευτον. σημεῖον δ᾿ ἱκανόν· οἱ γὰρ ἀγροῖκοι μάλιστα γνωμοτύποι εἰσὶ καὶ ῥᾳδίως ἀποφαίνονται.]

Aristotle (384-322 BC) Greek philosopher
Rhetoric [Ῥητορική; Ars Rhetorica], Book 2, ch. 21, sec. 9 (2.21.9) / 1395a.9 (350 BC) [tr. @sentantiq (2018)]
    (Source)

(Source (Greek)). Alternate translations:

In point of age, the use of maxims befit the old, and should be on those matters of which they have particular experience; so that for one who has not arrived at that stage of life, to use maxims is unbecoming; just it is for him to use fables; and if it be on matters whereof he has no experience, it is absurd, and a mark of ignorance. And the following is a sufficient proof of it, for that the rustics most of all are proverb-mongers, and are ready at uttering them.
[Source (1847)]

The employment of maxims becomes him who is rather advanced in life; and particularly as respects subjects about which each happens to be well informed. Since for one not so advanced in age to sport maxims is bad taste, just as it is for him to have recourse to fables: and the ue of them on subjects about which one is ignorant is silly, and argues a want of education. There is a sufficient sign of the truth of this; for the boors of the country are of all other people most fond of hammering out maxims, and set them forth with great volubility.
[tr. Buckley (1850)]

The use of maxims is suitable to elderly men, and in regard to subjects with which one is conversant; for sententiousness, like story-telling, is unbecoming in a younger man; while, in regard to subjects with which one is not conversant, it is stupid and shows want of culture. It is token enough of this that rustics are the greatest coiners of maxims, and the readiest to set forth their views.
[tr. Jebb (1873)]

The use of maxims is suitable for one who is advanced in years, and in regard to things in which one has experience; since the use of maxims before such an age is unseemly, as also is story-telling; and to speak about things of which one has no experience shows foolishness and lack of education. A sufficient proof of this is that rustics especially are fond of coining maxims and ready to make display of them.
[tr. Freese (1924)]

The use of Maxims is appropriate only to elderly men, and in handling subjects in which the speaker is experienced. For a young man to use them is -- like telling stories -- unbecoming; to use them in handling things in which one has no experience is silly and ill-bred: a fact sufficiently proved by the special fondness of country fellows for striking out maxims, and their readiness to air them.
[tr. Roberts (1924)]

The use of maxims is suitable for one who is advanced in years, and in regard to things in which one has experience; since the use of maxims before such an age is unseemly, as also is story-telling; and to speak about things of which one has no experience shows foolishness and lack of education. A sufficient proof of this is that rustics especially are fond of coining maxims and ready to make display of them.
[tr. Freese (1926)]

It is fitting for someone more advanced in age to speak in maxims, and about things he has experience of, since it is inappropriate for someone not of that age to speak in maxims, just as it also to tell myths, and to do so about things he is inexperienced in, this being a mark of foolishness and lack of education. There is a sufficient sign of this: country bumpkins are the ones most given to uttering maxims ....
[tr. Bartlett (2019)]