What the cut off age to join the Marine Reserves

Congress change the maximum age to 42 in 2006. However, different branches have different requirements. These are the maximum ages for non-prior service enlistment:

Active Army - 42
Army Reserves (Including National Guard) - 42
Active Air Force - 27
Air Force Reserve (including National Guard) - 34
Active Navy - 34
Naval Reserves - 39
Active Marines - 28
Marine Corps Reserve - 29
Active Duty Coast Guard - Age 27. Note: up to age 32 for those selected to attend A-school directly upon enlistment (this is mostly for prior service).
Coast Guard Reserves - Age 39.

Prior service enlistees can receive an age waiver.