St. Aloysius Gonzaga is the patron saint of young people and those struggling with purity.
St. Aloysius died young, at the age of 23, and is regarded as the patron saint of all young people.
Furthermore, his example of purity at such a young age remains an inspiration. For this reason he is invoked as a patron saint for those struggling with purity.
Here is a prayer from the Raccolta that asks for St. Aloysius' intercession for a pure mind and body.