It’s all in the legs.

That’s what Green Bay Packers coach Mike McCarthy believes will determine whether Aaron Rodgers — or any quarterback, for that matter — can do what Tom Brady is talking about: playing well into his 40s. New England Patriots owner Robert Kraft said this week that Brady would like to play six or seven more years.

Rodgers, 33, first indicated last offseason that he started to think of ways to maximize his longevity. That’s when he revamped his diet to, among other things, eliminate cheese and other dairy products. He also said he’s used Brady as a model for the way he eats and trains.

McCarthy said earlier this month at the NFL scouting combine that he wouldn’t be surprised if Rodgers was able to maintain his current level of play like Brady, who won the Super Bowl this past season at age 39. He took that a step further on Wednesday when he was asked at the NFL annual meetings if he could see Rodgers playing well into his 40s.

“I mean mentally and physically, clearly yes; he has that ability,” McCarthy told reporters in Phoenix. “I think there’s no question there. But I think all positions in football are the same. It’s their legs. You watch a player — and it’s no different with quarterbacks — as long as they have their legs, they can compete at that level.”

McCarthy, whose background is as a quarterbacks coach, doesn’t see any reason why Brady can’t keep going.

“I think you can only go by what’s on film and based on his last game, he will accomplish that,” McCarthy said. “I would bet on that. But there’s a lot of factors that go into that. I think you have to give these athletes an incredible amount of credit what they’re doing. With the rest and recovery and nutrition, I think you’re now seeing the decade of what it’s provided. It’s provided for guys to play longer, especially at that position.”

While some players have been retiring early due to long-term health concerns, McCarthy said he believes players have the chance now to play longer than ever due to increased knowledge about nutrition and training.

“If you do have good fortune and good healthy and you’re able to keep playing at a high level, I think these guys will play a lot longer than the generation before them,” McCarthy said.