In fact, fundamental theoretical physics has been more-or-less stagnant since the late 60's when the Standard Model was finished. But they have to keep handing out Nobel prizes. So the outcome is predictable: you see prizes being awarded to people who are fleshing out ideas which have been known for a half century; the low-hanging fruit has already been picked, so you have to work for years in the nitty-gritty to push the bounds. Hence, the prize winners are old.
But this doesn't tell us anything about physicists and when they are capable of genius (and how could it? does anyone really think that human nature has changed?), it tells us about the stagnation of the field.
The really interesting question is this: is the stagnation of physics more attributable to (a) some combination of fundamental technological/intellectual limitations or (b) institutional/social pathologies in Academia. Most people say '(a)', but I (as a young physicist) worry that '(b)' plays a substantial role.