Usually, a child attains puberty at the age of fifteen, however if he had experienced wet dreams before fifteen years in this case he would be considered matured from this time, and would be responsible to carry out all the Islamic commandments. If you were lazy in performing salah before you reached twenty, in this case you will have to perform the missed salah of five years. You can perform five missed salah after each salah. Keep on performing according to your ease. Your religious concerns are praiseworthy, may Almighty Allah make you pious and grant you steadfastness.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband