What is meant by a Young Person?

VATICANO_-_ISLAM_-_YOUNG_MUSLIM_PRAYING

Imam Jafar Sadiq (A.S) said to a man:

“What is meant by a young person [Al-Fata] in your estimation?”

The man replied, “A youth.” The Imam (A.S) replied, “No, the young person [Al-Fata] is the true believer. Surely the Companions of the Cave [Ashab Kahf] were all old people, however Allah, Glory and Greatness be to Him, called them youth who believed in Him.”

Al-Kafi, Volume 8, Page 395 and 595