I met my husband in college when I was 18 and he was 28. We were both freshman, both in very similar spots in life. We’ve been together for almost seven years now.
All of this to say that age gap relationships are tricky because until you are a fly on the wall you never know if it was a real bond or something nefarious. It’s easy to say “he’s taking advantage” from what we’ve got here, but OP actually gave us little to no information about him and their relationship.
OP my advice is to look at your relationship and compare it to a couple red flags lists out there. I know you said it’s more fwb, but I still think that’s a place to start. I would then introduce him to some of your close friends who you trust to tell you the truth. Friends will be able to see y’all interact, and if he is nefarious he might try to hide it less around friends than he would when meeting your parents.
All in all I’d say you are allowed to date him casually. Your age gap is just one part of the relationship, but it can be an indicator that other things are wrong. But with that being said you are also allowed to leave him. You’re allowed to trust your gut if you feel he isn’t treating you the way you want to be treated.
Best of luck OP, and good luck in college!