Guerrero made the comments Thursday on the Greg Hill Show on WEEI. Brady, 42, has completed 64.8 percent of his throws for 2,536 yards, 14 scores and five interceptions in nine starts this season for the 8-1 Patriots. The six-time Super Bowl champion has previously stated he wants to play into his mid-40s, but said that sentiment can always change.
Brady hasn't missed a start for injury-related reasons since the 2008 season.
"It all comes to commitment, really," Guerrero said. "No one thought you could play at the elite level in your late 30s, early 40s. That is something we always felt we could do. I have really wanted to be there to help him accomplish that goal. I certainly do believe that 45 is a very realistic goal.
"We talk about it all the time. Every year he just adds another year. He goes in and he's like, 'Guys, I feel so good still. I think I am going to go till 45.' I am like, 'OK.' Now he's like, 'Alex, I think I can go like 46 or 47.'"
Brady is set to hit free agency for the first time in his career this off-season. Guerrero said he does not know if Brady will be in training camp in July 2020.
Former kicker, quarterback and linebacker George Blanda holds the record for the oldest player in NFL history, when he played at 48 years old during his 1975 campaign with the Oakland Raiders. Blanda played 26 seasons in the NFL. Steve DeBerg was the oldest player to ever start a game at quarterback, when he appeared in a contest for the Atlanta Falcons at 44 years old during his 1998 campaign.
Brady has ranked inside the top six on the NFL Top 100 players list -- voted on by players -- every year since 2011. The future Pro Football Hall of Famer ranks No. 2 all-time in passing yards, passing scores, interception percentage and comebacks. He has started 40 playoff games, the most in NFL history.
Brady will suit up for his 279th career game and make his 277th career start when the Patriots take on the Philadelphia Eagles at 4:25 p.m. EST Sunday at Lincoln Financial Field in Philadelphia.