Does a person's intellect not become complete until after the age of forty?

Question : My soul is with the Messenger (peace and blessings be upon him) until he reached the age of forty. Is it known to us that a person does not bear full responsibility until after the age of forty?

Answer : Yes, that is correct. The perfection of intellect occurs at the completion of forty. meaning he completed [his development]. The scholars said this means he reached forty. Because before forty, one has not reached full maturity. Even if a person is among those with intellect and intelligence, he still needs experience. I mean, a person's mere intelligence and intuition are not sufficient in dealing with matters; experience is necessary.