Mmm...I'm not sure really.
So if we have the human uprising set thirty years before our plot, then he'd be about 50 or so perhaps? I'm thinking that around the age of 30 or 40 they become adults and are eligible for being elected but the humans interfered with this process and maybe he had been elected shortly before, when he was still quite young by their standards because the previous leader had been killed and no others fit the bill?

How old was your female going to be so I can kind of get an idea of how old he should be?