I am 33 and a junior at a large 40k+ campus. The best advice I have is to lean into it and embrace it. Odds are you don't look that much older, so it's not like people are going to really know unless you bring it up. But I embrace it by being the person in class that actively engages with the professor and classmates. Being older kind of automatically makes you a leader. 18 year olds are still in that high school mentality of "if I say something stupid people will laugh at me and I'll never get laid." We, older adults, don't have to give a shit about any social fallout.

Just don't be the person trying to be 18 again and don't be the old person that has to tell some personal story every time you raise your hand and you'll be fine.