Rob Gronkowski thinks Tom Brady could have played on until he was 50.
Brady had a short-lived retirement last year but confirmed he was calling time on his playing days for good on February 1.
The 45-year-old heads into retirement with seven Super Bowl rings, five Super Bowl MVP awards and three NFL MVP prizes to his name among countless records.
Gronkowski played alongside Brady for nine years with the New England Patriots and then linked up with the QB again for two seasons with the Tampa Bay Buccaneers.
He thinks Brady could have played at the top level for another five years.
"Yes, I was [surprised] but I wasn't at the same time," Gronkowski said.
"Football is a tough sport. But the only reason why I'm surprised that he's retired is because I think he could have easily played until like 50 years old, just the way he carries himself, the way he takes care of his body, just the way he preps every single week, week in and week out.
"At the same time, not really surprised. He had an unbelievable career. If you really think about a 45-year-old and was top three in passing yards... so he still went out on top, there's no doubt about it.
"Whatever he wants to do, whatever is going to make him happy, I'm going to support that."
Gronkowski, who retired after the 2021 season, is unsure where Brady might have ended up had he decided to continue his career.
"I don't know, wherever he decided but just loves the game of football," he added. "He just loves it so much. So I really wasn't sure what his plans were or anything.
"But I'm just super excited for him and just happy for him in whatever situation, he decides to do anytime."
Patriots chief executive Robert Kraft mooted the possibility of Brady ending his career at New England, potentially on a one-day contract.
Asked if he would be open to such a situation for himself, Gronkowski replied: "I think that offer's only open for Tom.
"I don't know. If it was offered and presented, it would definitely be a possibility. I love New England. I loved my time there. I've learned so much. I love Mr. Kraft. I love the whole organisation.
"Coach [Bill] Belichick, everyone, I've learned so much there over the nine years. So, if that was presented then that would definitely be something to consider. All because of just how much that place means to me for the rest of my life."