The Fleet Reserve and the Fleet Marine Corps Reserve are composed of members of the naval service transferred thereto under this section. An enlisted member of the Regular Navy or the Navy Reserve who has completed 20 or more years of active service in the armed forces may, at his request, be transferred to the Fleet Reserve.
A job notice or advertisement may specify an age limit only in the rare circumstances where age is shown to be a bona fide occupational qualification (BFOQ) reasonably necessary to the normal operation of the business.
At the age of 62, one can retire with social security benefits within the US, and is considered to be the age of a senior citizen by many organizations. However, the federal government has determined one who is 65 years of age or older is senior citizen. Organizations such as AARP and most businesses consider age 55 as senior citizen and you would receive the standard senior discounts. So there are various opinions, but age 55 is about the youngest considered age.