OP- it’s worth some time with your son helping him understand size and scope and what that means to an undergraduate. If a university has a law school, med school, forestry school, vet school-- all grad programs, many of which are not even on the same campus- that makes the place look really big- when in fact, the “on campus” population that will be part of his experience might be the same as a mid size college. You can spend four years as an undergrad and never once be in the same place as a medical student (they’re not going to football games!).
Help him focus on undergrad enrollment as a first cut.
Second- help him identify how much support he is getting right now. Not just formal support- how much scaffolding is the family providing? All that goes away once he’s living in a dorm. No roommate is going to toss him out of bed so he doesn’t miss his bio lab. No RA is going to keep him on task with his calendar, assignments, etc. So he’s got to come to terms with how much assistance he’s going to need to be “his best self” once he gets to college. Like many kids- he may be minimizing how much these informal supports have been critical to his success.
Where do you live and what is instate for you?