Obviously, school-aged children are required to keep up with their studies, either by working with a tutor, home-schooling, going to regular school, or going to a professional children's school. Once a child graduates from high school, they get to make their own choices. For example, several of the original cast members of SPRING AWAKENING deferred their admissions to college and began their studies after they left the show (Remy Zaken, Brian Charles Johnson). Gideon Glick was the first actor to leave the original company, and did so to begin college at NYU. Others skipped college all together.
Obviously, if you go to college in the city, it's a lot easier to perform while matriculating. If you went to school outside of the city or in another state, you would probably consider taking a leave of absence.
Some people start college and then leave once they begin to work full time. This is what happened with Laura Benanti, Ben Platt, etc. I believe Lea Michele said that she deferred her admission to NYU for something like 3 years before she realized that she was never going to go. Others (like Jennifer Damiano) who have been working since they were teenagers just decided not to go to school.
It's obviously a personal choice that each person has to make. In the case that the OP brings up, it's fabulous that his parents want him to continue his schooling, but he's an adult, and he has to make that decision for himself.
"You travel alone because other people are only there to remind you how much that hook hurts that we all bit down on. Wait for that one day we can bite free and get back out there in space where we belong, sail back over water, over skies, into space, the hook finally out of our mouths and we wander back out there in space spawning to other planets never to return hurrah to earth and we'll look back and can't even see these lives here anymore. Only the taste of blood to remind us we ever existed. The earth is small. We're gone. We're dead. We're safe."
-John Guare, Landscape of the Body