Twenty..
none, once a marine, always a marine.
10 years
USMC
No
A player is eligible for the Baseball Hall of Fame after being retired for five years.
6 months in the Marine Corps Reserve, and 23 years as a Civil Servant with the Marine Corps
5 years.
4 to 6 years
6 years
4 Undergraduate 2 years for Masters in Marine Bio 6 for PhD
General Kelly. Retired Marine Officer.
According to the article at http://www.slate.com/id/2139847/sidebar/2140026/, there are 82 on active duty, and 400 retired.