If he wants to be a Marine officer, do not enlist as a Marine enlisted Reservist. Have him talk to a local OSO and he can sign up for PLC which consists of two 6 week summer sessions that he completes after his sophomore and junior year at college and the he will commission as an officer after he completes his degree the following year.
There is certainly nothing wrong with enlisting, but he will be in a far better position post-Marine Corps career if he joins as an officer.
For your reference.
https://www.marines.com/becoming-a-marine/officer.html
I am currently a Reservist USMC Major and spent 11 years active duty as a Marine Corps F/A-18 instructor pilot. Shoot me any other questions you have.