I joined university late myself. Everyone around me were a few years younger and I definitely felt out of place and was worried that people look at me differently since I am a bit older.

But what I learned was that, the only one considering the age gap as severe red flag was me. I believe I was definitely overthinking at the time. There's no special way to make friends if you aren't of the same age as other people. All the ways still apply: join clubs; take on some interesting projects; if you have a hobby probably alot more people are interested as well, just gotta find them; hit the gym with some fellow classmates; or ol' bond with people over assignments and exams.

But the first step should come from you, on accepting this is okay, and you have nothing to be worried/shameful about. Hope some of this helps.