Is it permissible for a young man to benefit from money sent to him as Zakat, Kaffarat (expiations), and aid after he has become poor, knowing that he was not poor at the time the money was sent?

Firstly: You erred by holding onto the money, based on the Prophet's (peace be upon him) saying: "On the hand is what it took until it returns it," and by delaying the payment of zakat (definition) beyond its due time.

Secondly: If you are currently eligible for zakat, there is no harm in utilizing the money, provided you repent for withholding it and delaying its disbursement to those entitled to it.

Thirdly: When there was a need for the money, it was permissible to take it as zakat. Indeed, whoever possesses unsaleable goods and is in need of money, or owns goods, livestock, or crops that are insufficient for their needs, is permitted to receive zakat. Imam Ahmad said: "If he has an estate or real estate that yields ten thousand or more, but it is not sufficient for him, he may take from zakat." The self-sufficiency that prevents one from receiving zakat is that which provides sufficiency. If one is in need, zakat becomes permissible for them, even if they own a nisab (definition) or more.