The question of “How long will Tom Brady play?” remains one of the most important questions in all of New England sports.

Most of the time, the default answer has been that the Patriots quarterback plans to play until he’s 45 years old. For the immediate future, he’s set to play at least the 2019 season in New England.

But where’s the stopping point? In the NFL, the future remains uncertain. But Alex Guerrero, Brady’s business partner and training guru, is ambitious in declaring that the 41-year-old quarterback has plenty left in the tank.

On Tuesday, Deadspin published an excerpt from the book “No One Man Should Have All That Power: How Rasputins Manipulate the World," by Amos Barshad.

In the excerpt, Guerrero explains his relationship with Brady, with whom he started the TB12 Sports brand. Guerrero told Barshad that he calls Brady his “best friend” and says he thinks Brady can “absolutely” play until he’s 45.

From Deadspin:

“I know how Tom feels every day,” Guerrero assures me. “He says, ‘I don’t have any soreness. I’m ready to play again. Those are things that we thought would happen, and now we’re seeing the reality of them happening. Do I think Tom can play to a high level at forty-five? Absolutely.”

“OK. How about fifty?”

Barshad then followed up by asking if Brady could play until he’s 50.

More from Deadspin:

Guerrero laughs. “I mean, why not? I’ve never put limits on myself, and I’ve never put limits on any of my clients. I’m a big believer that everything is learned behavior. You tell an athlete, ‘You’re gonna be done when you’re thirty,’ well, the brain begins to believe that, and all your neuro-programming is based on, ‘OK, I’m thirty, I’m old.’ But I don’t think the brain understands the concept of time. It doesn’t understand age. Right? How would your brain know you’re whatever age you are? I always tell Tom, we’re not gonna tell our body what we wanna do. We’re gonna tell our body what we want it to do.”

Guerrero has a unique role in regards to the Patriots and Brady and has been a source of drama around the organization. Guerrero, who is not employed by the team, is regularly around the team and has a number of players as his clients. At times, he’s had enhanced access to the time, while he’s also had those privileges revoked by Bill Belichick.

Guerrero’s training methods have reportedly been at odds with that of the Patriots. Brady has regularly faced questions about Guerrero’s role and troubled history has a medical practitioner, but has typically dodged them.