How old is Hades, physically?

Simple answer? Let’s call him twenty-five.

Less simple answer? While Persephone said she thinks he’s in his mid-twenties, the answer to that question is going to depend on which part of Hades you’re talking about. The gods are basically frozen in their prime. That moment before cells start degrading and everything is just getting better and better and better. For different parts of your body or brain, that turning point happens at different parts of your life. For instance, your prime years of math learning or foreign language learning are over way before your prime height. But for simplicities sake, human men stop maturing in their mid-twenties, exactly which year/month/day of their mid twenties is going to vary person by person, but mid-twenties is a pretty safe estimate.