Is it obligatory to make up missed prayers, and what is the correct way to pray for a 23-year-old who wishes to commit to them after a period of discontinuity?

Neglecting prayer is a grave sin, and its offense is greater than adultery, consuming alcohol, and taking a life. Many scholars have even gone to the extent of declaring that one who abandons prayer commits an act of disbelief. People's opinions are not an excuse for abandoning it. One must hasten to sincere repentance, for Allah accepts the repentance of His servant and forgives his sins. As for making up intentionally missed prayers, it is a matter of scholarly disagreement; the more cautious approach is to make them up in a way that does not harm one's body or livelihood. However, there is no need to make up missed fasts if they were observed.