We live in an age of NFL parity. That's the nature of a league that has a short average career span, a salary cap, a crapshoot draft and free agency. It's hard to sustain greatness (or awfulness) for a long time.

The New England Patriots are the obvious exception to that rule, but New England and several other heavyweights led by legendary quarterbacks soon could be forced to rebuild.

The Super Bowl windows for the following six teams appear to be nearing their end.

Pittsburgh Steelers

Pittsburgh Steelers quarterback Ben Roethlisberger turned 37 in March, although he says he wants to play for at least three more seasons.