Thou knowest the errors of unripened age,
Weak are its counsels, headlong is its rage.

[οἶσθ᾽ οἷαι νέου ἀνδρὸς ὑπερβασίαι τελέθουσι:
κραιπνότερος μὲν γάρ τε νόος, λεπτὴ δέ τε μῆτις.]

Homer (fl. 7th-8th C. BC) Greek author
The Iliad [Ἰλιάς], Book 23, l. 589ff (23.589-590) [Antilochus to Menelaus] (c. 750 BC) [tr. Pope (1715-20)]

(Source (Greek)). Alternate translations:

You, more in age
And more in excellence, know well, the outrays that engage
All young men’s actions; sharper wits, but duller wisdoms, still
From us flow than from you.
[tr. Chapman (1611), l. 505ff]

Thou know’st how rash is youth, and how propense
To pass the bounds by decency prescribed,
Quick, but not wise.
[tr. Cowper (1791), l. 729ff]

Thou knowest of what sort are the errors of a youth; for his mind is indeed more volatile, and his counsel weak.
[tr. Buckley (1860)]

Thou know’st the o’er-eager vehemence of youth,
How quick in temper, and in judgement weak.
[tr. Derby (1864)]

Thou dost know
The faults to which the young are ever prone;
The will is quick to act, the judgment weak.
[tr. Bryant (1870)]

Thou knowest how a young man's transgressions come about, for his mind is hastier and his counsel shallow.
[tr. Leaf/Lang/Myers (1891)]

You know how easily young men are betrayed into indiscretion; their tempers are more hasty and they have less judgement.
[tr. Butler (1898)]

Thou knowest of what sort are the transgressions of a man that he is young, for hasty is he of purpose and but slender is his wit.
[tr. Murray (1924), l. 589-90]

It is easy for a youngster to go wrong from hastiness and lack of thought.
[tr. Graves, The Anger of Achilles (1959)]

You know a young man may go out of bounds:
his wits are nimble, but his judgment slight.
[tr. Fitzgerald (1974)]

Well you know how the whims of youth break all the rules.
Our wits quicker than wind, our judgment just as flighty.
[tr. Fagles (1990)]