I understand this sentiment entirely, but I think we have enough promising younger players, with a lot of hype around them. What we still lack are players in the prime of their careers, or about to enter their primes. I'm talking about top class players in the 23-29 age range. I think we need to go a step beyond players who are young, a la Dembele etc., and more towards players who have time on their side, but have made that big breakthrough and already established themselves. Players like Carrasco, who have gone through the growing pains already, learned their trade, and are on the cusp of potentially being brilliant.
Mourinho is the first manager, since Fergie retired, to buy players of the requisite quality or potential, and at the right age (Zlatan aside). Moyes had two panic signings, and Van Gaal signed so many average, disinterested or ill fitting players, it defies belief.