Nowhere can we find an exact age or timeline regarding Milo's age. The consensus is 16-21 from fans, though. It's safe to say he's above ten, which is the median or general age of trainers, and while there are young Gym Leaders, he is known as a kind, caring, almost cool cousin type of guy in town, and has said to have trained many people, so he has he be on the older side. It is still debatable what exact age he is, even if we make a decent guess.