Is playing until 40 (or more) the next tide of the NFL?

Tom Brady, soon Big Whit, and now Trent Williams is thinking 40 is his target.
We're seeing some aging QBs like Aaron Rogers who it seems just keeps getting better with age. I think some positions won't allow it to happen due to the pounding they take (R, but at WR Larry Fitzgerald is getting pretty long in the tooth and while he's lost a step he's still pretty effective.

I think some of it might be a changed expectation and so a bit of a state of mind in that if a person remains bought-in to playing, still has the fire, and is physically able to play to 40, then perhaps the question for them becomes: why not? Certainly for the majority they'll never make the kind of money once they retire that playing pays (even at $1 or $2 mil per year).

Some, most, will probably just grow tired of the grind. Others won't be good enough to be kept around that long. But others... the really good ones.... may well rethink the possible length of career and take action to keep their bodies as sound as possible. Of course, HCs will have to play along as well and consider age in workouts and maybe even playing time.