You said something about enlisting and going to OTS. Remember to make the distinction. If you want to be an officer do not, repeat, do not enlist. You just go to OTS. About the age limits:
USAF: Must meet a selection board before age 28 1/2. Must enter Undergraduate Flying Training (UPT) before age 30.
USN/USMC: To become a Naval or Marine Corps Aviator, you must be between the ages of 19 and 26 at the time you enter flight training. Adjustments (waivers) can be made up to 24 months for those with prior service, and up to 48 months for those already in the military at the time of application.
USCG: The Coast Guard does not accept pilot applications, unless the person has already been a military pilot in a different service. To apply, one must be over 21 and under 32 years of age, must have at least 500 hours as a rated military pilot, and must have full-time flying experience within two years of the application.
If you like helicopters, too, here is some information about the United States Army: Must not have reached the 29th birthday as of the date of the convening board. Must not have reached the 30th birthday as of the date entered flight training.
So, generally, you're in luck.
I have heard that you can get a flight contract in OTS, but I'm not sure how. I'm on a forum at www.fighter-pilot.org and there are some people there that can probably give you better information than I can. Anyways, unless you like helicopters, I think that you would really do the best in the USAF since you are still under the maximum age limit for pilot training. So that means that you'd definitely have some room to get a flight slot.