Matt Birk announces retirement

The Baltimore Ravens' Matt Birk wrapped up one of the most distinguished careers for an NFL center, announcing his retirement Friday just 19 days after winning the first Super Bowl of his 15-year career.

A sixth-round draft pick out of Harvard, Birk was selected to six Pro Bowls in his career. He helped the Ravens establish a franchise record for points this past season, started for the NFL's top-ranked offense in Minnesota in 2003, and blocked for Adrian Peterson in 2008 when he won his first rushing title. Birk finished his career with 112 straight starts, the longest active streak among centers.

"I'm old," Birk told students at a Baltimore elementary school on why he was retiring, according to the team's website. "I've got six kids. It's time to do something else."

Birk's announcement was expected to come this offseason. He would turn 37 at the start of this year's training camp, and the Ravens drafted his eventual replacement, Gino Gradkowski, in last year's draft. The Ravens save $2 million on the salary cap with Birk no longer on the roster.

"We were all so fortunate to have Matt Birk as a Raven - the team, everyone in our building, the community," Baltimore coach John Harbaugh said. "It was a privilege to coach him and an honor to have him as a friend. We are better people for being around Matt, blessed in fact. Young players could watch Matt and know that was how to be an NFL professional."

Unlike linebacker Ray Lewis, Birk wanted time to think about his decision before making it official Friday.

"I have absolutely nothing to complain about and a lot to be grateful for," Birk told The Baltimore Sun during his community event.

Birk won the NFL's Walter Payton Man of the Year award in 2011 for his community service and has said he is planning to donate his brain to science to aid research on sports concussions.