Before I reached the age of puberty, my mother said I offer Salah too fast, so when she was in the room, I used to stay in Qayam for a bit after reciting Suraahs and then go to sajidah.
There are two groups of ignorant in Islam:
1.Culpable ignorant: People who have failed in fulfilling their duties due to negligence and irresponsibility. For instance, Although they are fully aware of being obliged to a certain set of duties, they are too irresponsible to make any effort to find out about them.
2.Inculpable ignorant: People who have failed in their obligations in spite of the fact that they have tried their best to find out about them.
Although one of the condition without which one cannot be considered among sinners is awareness(to be fully aware that, for instance, watching porn movies is a sin), the first group will definitely be among sinners and the blame of this ignorance lies with them owing to them being negligent and irresponsible.
The second group will not receive any punishment but in certain cases they have to make up for the obligations they have failed in. For example, not offering the daily prayers in the prescribed times.
There are just a few cases in which even the first group is not obliged to compensate for anything. For instance:
It is Wajib(obligatory) for a man to recite Surah al-Hamd and the other Surah loudly, while offering Fajr, Maghrib(sunset) and Isha prayers, and it is Wajib for a man and a woman to recite Surah al-Hamd and the other Surah silently while offering Zuhr(noon) and Asr(afternonn) prayers. (Source)
However, if a person recited loudly where he should recite silently and vice versa, his prayer would be in order as long as he has not recited so intentionally. So he does not have to make up for his prayers even though he is a culpable ignorant about this rule.
And Last but not Least: one is free from any responsibilities and obligations as long as he or she has not reached puberty. However, people's right is the only exception which means that if an immature person (for example) stole something, he or she would be obliged to return it or pay a compensation for it as soon as he or she reaches puberty even though this person is not considered a sinner.
No. Al-bagharah 286. You will be asked due to your abilities.
Solution is tobah (repentance) and never do the sin again God is the greatest forgiver.
But take care after tobah if your sin damaged anybody you should take care of him/her and recover the damage. God will not ignore human rights which damaged by you in next world even after tobah. But if you stay on your tobah inshallah he will ignore his rights you broke with your sin.