How the fuck do you get your 19 year old son to stop staying up until 3am and then sleeping till 2pm?

He has a job, and he goes to it, and he's going to re-enrole back in college classes in the fall. But it's like all he does is hang with his friends and his roommate and play computer games or go to the gym every night. I've been trying to motivate him to get out there and do more things, but nothing seems to be working. I'm stuck. Any suggestions?