Each of the services have different age requirements to become a pilot or navigator.
Navy and Marine Corps
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.
Must meet a selection board before age 28 1/2. Must enter Undergraduate Flying Training (UPT) before age 30.
Army (Rotary Wing)
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.
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.