Before 2270, the Federation Starfleet had a policy of mandatory retirement set (for humans) at age 75.
When in 2270 Commodore April proved that he was still very much capable of commanding a starship at 75, Starfleet reviewed it's retirement policy and abolished it. April was allowed to continue his work. (TAS:"The Counter-Clock Incident")
Another example was Leonard H. McCoy, still a Starfleet admiral at age 137, in 2364. (TNG:"Encounter at Farpoint")