33 U.S.C. § 3044
Retirement for length of service
An officer who has completed 20 years of service, of which at least 10 years was service as a commissioned officer, may at any time thereafter, upon application by such officer and in the discretion of the President, be placed on the retired list.
( Pub. L. 107–372, title II, § 244 , Dec. 19, 2002 , 116 Stat. 3089 .)