Assalamualaikum sheikh,hope you can answer my question when you see this question.if a person apostatized before he reach the age of puberty he will not accountable of it.But what if a person reach the age of puberty but dont know that it was sign of puberty ,will his apostate be valid?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Puberty is known through certain signs, such as the growth of pubic hair, ejaculation of semen, or reaching the age of fifteen Hijri years. So, whoever reaches puberty becomes a Mukallaf (a legally competent, obligated person), and thus is required to observe all rulings required under Takleef though he might not be aware that he has reached puberty. Ignorance in this case is considered a mistake committed by this person as he did not seek after knowledge. As such, the person would not be held accountable for any sins, including disbelief he committed before reaching puberty, rather, his accountability starts from the very moment of reaching puberty.

Allah knows best.