Language is important here.
Agreed, probably best at this point to break it down by service.
Marines
Two kinds of retirement, Active Duty and Reserve.
Active Duty Retirement - Normal 20 year / 50% pay as soon as you retire, more if you stay longer. You will get this if you retire from Active Duty or Active Reserve in the Marines (20+ years)
Reserve Retirement - Eligible after you complete 20 satisfactory (SAT) years in the armed forces. For pilots, this will usually include a mix of active duty and selected Marine Corps reserve (SMCR) time. I know a few who have some IRR SAT years in there as well. This is the retirement that kicks in somewhere around 60 years old.
Three kinds of Service
- Individual Ready Reserve (IRR). This is the most common reserve experience, which in most cases is a paper drill and doesn't require a lot of (any) participation. When you EAS typically you go right into the IRR and stay there until HQMC cuts the cord completely. You can get to the reserve retirement by getting 50+ points a year to have a SAT year, but you won't be paid for your monthly participation.
- Selected Marine Corps Reserve (SMCR). As a pilot, if you EAS and then affiliate AS A RESERVIST with a reserve unit, then this is your category. You also will get the reserve retirement. If you do a one year or longer mobilization (ADOS) you are still an SMCR reservist, and rate the reserve retirement when you turn 60. You get paid to drill and accrue retirement points.
- Active Component. ACTIVE DUTY folks or those who EAS and join the ACTIVE RESERVE from the IRR/SMCR/AD fall into this category. Active Reserve in the Marines is the same as FTS for the Navy/Air Force. AD/AR rate the active retirement as soon as they hit 20 years of service and their retirement is approved.
- Be careful here, there is something in Guard Units called a Technician Pilot, which sounds a lot like AR/FTS but is a GS-12/13 position with a Reserve Commission in the Guard. Retirement in this case is the Reserve Retirement which again, doesn't kick in until 60.
For Marines, read the MCRAMM if you really want to nerd out on reserve stuff:
http://www.marines.mil/Portals/59/MCO 1001R.1L.pdf