Is a young man considered an apostate for leaving Islam due to abandoning prayer and fasting, and is it obligatory for him to renew his Islam, make up all missed prayers, and offer expiation for fasting for past years, knowing that he has performed Umrah and prayed for guidance?

Abandoning prayer and fasting is a grave sin. Prayer is the pillar of religion, and abandoning it is disbelief. Fasting is one of the pillars of Islam, and not observing it without a valid excuse is one of the major sins. Engaging in masturbation or other sins is not an excuse for abandoning prayer and fasting. The questioner's feeling of guilt and prayer for guidance is good, but it is not enough. One must hasten to repent to Allah and make up for what has been missed, for Allah Almighty is vast in mercy and forgives all sins. Repent to Allah with sincere repentance, and make up for the prayers and fasts you have missed according to your ability.