10 U.S.C. § 1209

Any member of the armed forces who has at least 20 years of service computed under section 12732 of this title , and who would be qualified for retirement under this chapter but for the fact that his disability is less than 30 percent under the standard schedule of rating disabilities in use by the Department of Veterans Affairs at the time of the determination, may elect, instead of being separated under this chapter, to be transferred to the inactive status list under section 12735 of this title and, if otherwise eligible, to receive retired pay under section 12739 of this title upon becoming 60 years of age.