A man at five may be a fool at fifteen.

A child’s apparent intelligence or good sense does not reliably predict how he will behave later. Early promise should not be treated as a permanent measure of character or judgment.

The saying cautions against assuming that maturity develops in a straight line. Someone who seems unusually sensible when young may still make foolish choices at a later age.

Used when discussing a young person whose early maturity or ability should not be taken as a guarantee of lasting wisdom. It can temper confident predictions about how someone will develop.