Paul, 1 Corinthians 13.11:
When I was a child, I spake as a child, I understood as a child, I thought as a child: but when I became a man, I put away childish things.
ὅτε ἤμην νήπιος, ἐλάλουν ὡς νήπιος, ἐφρόνουν ὡς νήπιος, ἐλογιζόμην ὡς νήπιος· ὅτε γέγονα ἀνήρ, κατήργηκα τὰ τοῦ νηπίου.
Teles, On Self-Sufficiency
, p. 10 of Teletis Reliquiae
, ed. Otto Hense, 2nd ed. (Tübingen: Mohr, 1909):
You have become an old man; don't desire youthful things.
γέρων γέγονας˙ μὴ ζήτει τὰ τοῦ νέου.
Epictetus 3.24.53 (tr. W.A. Oldfather):
When a person acts like a child, the older he is the more ridiculous he is.
ὁ τὰ παιδίου ποιῶν ὅσῳ πρεσβύτερος τοσούτῳ γελοιότερος.
Seneca, Letters to Lucilius
27.2 (tr. Richard M. Gummere):
I keep crying out to myself: "Count your years, and you will be ashamed to desire and pursue the same things you desired in your boyhood days."
Clamo mihi ipse: "Numera annos tuos, et pudebit eadem velle, quae volueras puer, eadem parare."
Seneca, On Firmness
12.1.1-2 (tr. John W. Basore):
The same attitude that we have toward young slaves, the wise man has toward all men whose childhood endures even beyond middle age and the period of grey hairs. Or has age brought any profit at all to men of this sort, who have the faults of a childish mind with its defects augmented, who differ from children only in the size and shape of their bodies, but are not less wayward and unsteady, who are undiscriminating in their passion for pleasure, timorous, and peaceable, not from inclination, but from fear?  Therefore no one may say that they differ in any way from children. For while children are greedy for knuckle-bones, nuts, and coppers, these are greedy for gold and silver, and cities; while children play among themselves at being magistrates, and in make-believe have their bordered toga, lictors' rods and tribunal, these play in earnest at the same things in the Campus Martius and the forum and the senate; while children rear their toy houses on the sea-shore with heaps of sand, these, as though engaged in a mighty enterprise, are busied in piling up stones and walls and roofs, and convert what was intended as a protection to the body into a menace. Therefore children and those who are farther advanced in life are alike deceived, but the latter in different and more serious things.
Quem animum nos adversus pueros habemus, hunc sapiens adversus omnes, quibus etiam post iuventam canosque puerilitas est. An quicquam isti profecerunt, quibus <puerilis> animi mala sunt auctique in maius errores, qui a pueris magnitudine tantum formaque corporum differunt, ceterum non minus vagi incertique, voluptatium sine dilectu adpetentes, trepidi et non ingenio sed formidine quieti?  Non ideo quicquam inter illos puerosque interesse quis dixerit, quod illis talorum nucumve et aeris minuti avaritia est, his auri argentique et urbium, quod illi inter ipsos magistratus gerunt et praetextam fascesque ac tribunal imitantur, hi eadem in campo foroque et in curia serio ludunt, illi in litoribus harenae congestu simulacra domuum excitant, hi ut magnum aliquid agentes in lapidibus ac parietibus et tectis moliendis occupati tutelae corporum inventa in periculum verterunt. Ergo par pueris longiusque progressis, sed in alia maioraque error est.
puerilis add. Gertz
I'm indebted for knowledge of these parallels to Walter C. Summers, ed., Select Letters of Seneca
(1910; rpt. London: Macmillan and Co., 1952), pp. 190-191, who cites Teles from p. 6 of Hense (perhaps another edition).