Well! I think he's about 17 actually. I think Karen was his first wizard. Because he said "You restored my faith in celestial wizards". Plus if he was really old, I dout he would have a crush on Lucy. Because he loves her and it's obvious. I dout if he was like really old that love would exist.
When I check the wikia, they never mentioned his age. So we really do not know, but since he is a celestial spirit, maybe they are ageless or something, because they are spirits. For example in this picture, you see Aquarius, Capricorn and Cancer with Layla, Lucy's mother. But if you see them now with Lucy, they are still the same. So maybe they are ageless or something. But whatever their age they are really good friends !!! :) I hope you like my answer !!!!! :)
