If a young boy goes for Hajj and enters into the state of ihram, then reaches the age of maturity (puberty)…

Answer

In the name of Allah, if he reaches the age of maturity (puberty) before reaching the specific points (miqats) for entering ihram, he should renew his intention and enter ihram from one of the designated points or from outside the sacred precincts of the Haram, following the usual procedures. He is then obligated to perform the obligatory Hajj as a fundamental of Islam, provided that he has the financial means to do so. Allah knows best.