I wouldn't go that far! Most keepers don't really develop until they are around 23, so I think it'll be a while for him.
Tho to be fair, having seen replays of the goals from yesterday he was far from the only one to blame. For the first goal neither of the centre backs talked to him at all. Smalling or Evans should just have told him to ignore the players and focus on the ball - they were all too preoccupied with what the Liverpool players on the keeper were doing, and Carrick should have done a much better job against Agger. And for the second goal Smalling's positioning was woeful - he dropped right out of the line when he should have been tight to Bellamy and thus playing Kuyt offside.
Still, these are the kind of things that will happen when you have such an unsettled back line. As Szcesny, Koscielny and Mertesacker have shown at Arsenal, even the dodgiest defenders can build a decent foundation when they can play together for 10-15 games in a row. Whereas yesterday was the first time De Gea, Evans and Smalling have ever played together as GK and CBs. And Evans and Smalling are hardly the most complementary pair of CBs around!