The traditional rule is one month of age waiver for every month of active duty, so a full four years buys you up to 31. Remember that this is a Waiver "request", they don't have to give it to you, but generaly they do. They'll want to see your DD214 (if pior) and check out the months column for your service. If age is a factor you might want to consider the Marines, they tend to overlook age for VERY qualified people.