Three quarterbacks took turns throwing as the New England Patriots began training camp Thursday.

It’s the 15th for Tom Brady, the fourth for Ryan Mallett and the first for Jimmy Garoppolo.

All had plenty to learn.

“It’s about making improvements and I think it goes from the guy who’s the newest on the team to the guy who’s the oldest on the team,” Brady said. “I don’t think you ever have it all figured out.”

Less than two weeks before his 37th birthday on Aug. 3, the two-time Super Bowl MVP participated in the first practice of camp. When the session, lasting more than two hours, was over, sweat dripped off his face as he was surrounded by reporters.

At his first Patriots camp in 2000, Brady was hardly the center of attention after being drafted in the sixth round. He threw only three passes that season, the fewest of any of the three backups to Drew Bledsoe.

Now he’s the oldest Patriot by more than three years but retains his youthful energy and drive.

“It goes pretty fast so I think you just appreciate it and there’s very few people that have the opportunity that I have and I’m very appreciative of it,” Brady said. “You never know when the last one’s going to be, so you just appreciate the moments that you have.

“Every year is something different and this could be your last training camp. You never know. So you’ve got to make it count and you can’t take anything for granted in the NFL. So I try to do the best I can for this team and, hopefully, it leads to a great year.”

Brady did not have a great year in 2013.

His completion percentage of 60.5 was his lowest in 10 seasons. Excluding 2008, when he suffered a season-ending knee injury in the opener, his passer rating of 87.3 was his lowest in nine seasons and his 25 touchdown passes were his fewest in six.

He had four new receivers last season, veteran Danny Amendola and rookies Aaron Dobson, Kenbrell Thompkins and Josh Boyce. He has some experience with them now but there’s still a long way to go for them to join Julian Edelman as a serious threat to defensive backs.

“There’s always a lot of work,” Brady said. “I don’t think there’s ever a day you could take off. Especially with the limited amounts of practice that we have, you have to make them all count. You have to make the walkthroughs count. You have to make the practices count. You have to make the meetings count and each one of them becomes more and more valuable.”

He’s also getting reacquainted with his best pass catcher, Rob Gronkowski. The tight end played only seven games last season, missing the first six after forearm and back surgeries then suffering a season-ending knee injury in the 13th game.

On Thursday, Gronkowski ran pass patterns and had a serious look when watching others go out for passes. There were few smiles from the hard-working, fun-loving star.

“If he’s not out there, we’ve still got to find a way to do it. I think, really, that’s the lesson that we’ve learned,” Brady said. “We’ve got to try to win no matter who’s out there. You’ve got to find a way to compete at a high level.’

Thompkins had a strong practice Thursday, diving to make a few catches.

“It’s exciting for a quarterback when you see a guy make those type of efforts, lay out and catch the ball like he did,” Brady said.

The free agent rookie last season had 32 catches in the Patriots first 12 games. But in the last six, including two in the playoffs, he was inactive in four and had no receptions in the other two.

“He’s another guy that’s put a lot of work in and fought really hard,” Brady said. “There’s nothing that’s ever been given to him.”

Brady wasn’t a highly touted rookie either. Now, 15 years later, one of the NFL’s best all-time quarterbacks is determined to get even better.

“You work hard to put yourself in a good position to compete and when you get your opportunity you’ve got to go out and make it happen. So it’s really everybody. There’s nobody that’s immune to it. You’ve got to put the work in.

“This game is a very humbling game,” Brady said. “You’ve got to go out and prove it every single day.”

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