I think you have to put it in context: Carwin does have 2 losses in a row but they're to 1. The current champion at the time Lesnar (who was ranked #2/currently #3) and 2. The #1 contender JDS (currently ranked #4/most likely #4 or #3 now). So he's only lost to the current best of the best in the HW division.
There's still plenty of guys Carwin would destroy, namely Pat Barry, Kongo, Struve, Browne, Hunt, Rothwell, Nelson, Big Nog, Mir (again), Schaub (teammates, but if they fought).
I don't think he's hit "gatekeeper" status just yet. But if he loses his next couple fights you might just see him retire because I agree his age IS a problem.