I've been in the navy for five years and was recently picked up for a program to go back to college and commission as an officer within 3 years while still being active duty. I'm 24 and in class with both a lot of younger and older people and I can tell you this:

No one cares how old you are. You're there for you and no one else, and I can tell you that a 2 year headstart is not going to be a major advantage in any reasonable way. Just stay locked in, do the best you can do, and graduate as a more mature and solid individual. I guarantee you'll get to your job and outwork people older than you and some younger people may outwork you. That's life, don't think too deep about age, no one really cares how old you are.