Will a person be held accountable for harming others and throwing stones at people's trees in childhood, during a period when they do not remember whether they reached puberty or not? And what is the age determined by scholars for a person to be considered accountable if they are unaware of the time of their puberty?

The signs of puberty are reaching fifteen years of age, or ejaculation, or the growth of coarse hair. If you doubt whether an action occurred before or after puberty, the default assumption is that it was before puberty. As for financial liabilities, such as damaging fruits, financial compensation is obligatory by paying the value of the fruits to their owner, or by giving charity on his behalf if it is not possible to deliver them to him. There is no accountability for neglecting istinja' (washing after defecation/urination) before puberty. After puberty, if it was due to ignorance, the prayer is not invalidated according to the sounder opinion, and there is no need for قضى (making up the prayer). However, if it was done knowingly and with ability, then the prayer must be made up. Ibn Taymiyyah held the view that whoever neglected a condition of prayer due to ignorance does not need to make it up.