he started using the Batman Beyond costume?
I'd rather him start making the suit at 17 years old, it would make more sense like that. He has the smarts and the skill to make a Bat suit, like the one above. Or Bruce could have made that Bat suit for Tim Drake, and when Damian returns he could steal it. I think this would make a good origin for the Batman suit, if it already doesn't have one. Or Tim Drake could have made the suit for himself, that could be believable. I doubt Damian would use this suit if he returned.
So what do you guys think?