I sure he did and I'm sure he'd be good there but it's clear he's best as a #10. Januzaj may well be a kid, but it's clear he's a great player already. If you're good enough you're old enough.
Rooney is a better player than Mata. If Rooney stays it's not worth the money. If Rooney goes, then by all means, please send Mata this way.
Personal opinion and all that, I guess.