My son, young men’s arms are indeed taut for action, but old men’s counsels are better; for time teaches the most subtle lessons.

Euripides (485?-406? BC) Greek tragic dramatist

Bellerophon [Βελλεροφῶν], frag. 291 (TGF) (c. 430 BC) [tr. Collard, Hargreaves, Cropp (1995)]
    (Source)

Alternate translation:

Son, the hands of young men always itch for action, but the
judgment of the old is sounder.
Time teaches discrimination
[tr. Stevens (2012)]