No advantage because of age if you haven't been playing in over a year. You'll be somewhat out of "hitting" shape and practice shape when you take the field, and unless you've been doing gassers or field sprints in full clothing you'll be out of the loop as well for at least a few days. Some colleges have 3-a-day practices in the summer and most h.s. kids have a tough as hell time adapting to that even with the benefit of having played all the way through at least four seasons consecutively.
Depending on the program you'll likely have to do certain qualifiers just to be able to put pads on to try out: timed 100 yard sprint, coordination drills, etc. If you've been doing that then you'll probably be fine for the go ahead to do dress tryouts. However, it will also depend on your size and what positions you played in h.s. You might want to have your h.s. coach (if you and him got along) talk to someone in the program just to have someone know you're there. It's not always about how good you are especially if two or three other guys are trying out for the same position, so a good word from a coach can help out there.
We had a few guys who were older and some of them cut the mustard just fine. Other than joking around about old man and such it's no big deal. If there is any advantage at all in being a year or two older I can't think of any...besides, if competition to make the team is high then everyone is going to be hitting as hard as they can to impress the coaches. I forgot to add that on most college squads every player on the team was one of the top two or three players on his h.s. team in my opinion, just so you'll know what you may be up against. Lots of great players walked on and did well. Just because a scout didn't pick you up doesn't mean squat. Go get em like Tx said.
By the way, what positions have you played?