Some sources claim Leo is 30, but I haven't found solid evidence so its up in the air. Most people didn't know Kefka was 35 until Dissidia mentioned his age, so I would gather there may not be an official name. Hell, I keep finding conflicting information on Gestahl's age.

As for not recruiting Locke, I never actually tried but I must say, all the awesome fan-art of Setzer and Celes kinda make me wish the game had explored that relationship better.