let me put it that way: It's not guaranteed you'll ever get a playerwho is this good again. On the other hand, he's definitely a C, and for a DV team, those guys get too expensive very fast.
It's a hard decision, but if I was you, I'd sell him, and buy a good trainer, some more arena seats and three other 18yo guys (preferably guards) with a bit less potential for the revenue. Then train your new Guards for now.
If you need more help starting, just ask either here in the forum or per BB-Mail :)