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PHILADELPHIA -- Jason Kelce, who retired Monday after 13 NFL seasons -- all with the Philadelphia Eagles -- is going to be remembered as one of the greatest centers in NFL history. The only center to earn six First-Team All-Pro honors and win a Super Bowl title, Kelce solidified his Hall of Fame status when he earned his final All-Pro selection in his final season, separating him from many of the all-time greats at his position. 

Kelce earned all six of his First Team All-Pro selections in his 30s, the most ever by any player in his 30s (Jerry Rice and Bruce Smith are second with five). He went out at the top of his game, earning three First Team All-Pro honors in his final three seasons. Kelce and Dwight Stephenson are the only two players in the Super Bowl era to earn three consecutive First Team All-Pro and Pro Bowl selections in each of their final three seasons. 

While it's hard to measure Kelce's greatness with the other legendary centers in NFL history, ProFootballReference.com's Approximate Value (AV) is one measuring tool. Approximate Value is an attempt to put a single number on the seasonal value of a player at any position from any year (since 1960), but it's also greater based on number of games and seasons played. 

Mike Webster has the most seasons of a 15+ approximate value (four), but Jim Otto has the most seasons with 10+ approximate value (12). The statistic is difficult to measure, but Kelce is classified amongst the all-time greats at center. He also has the second-highest approximate value for any center who's played fewer than 200 games. 

How does Kelce stack up against the great centers? This isn't a definitive ranking, more of a list compiled by a way to compare eras using Approximate Value. 

Jim Otto (163 AV)

Arguably the greatest center in NFL history, Otto earned 10 First Team All-Pro selections and 12 Pro Bowl selections in his 15-year career with the Raiders, both the most by a center in NFL history. A First Team All-Pro in 10 of his first 11 years, Otto started all 210 games he played -- never missing a game. 

Mike Webster (161 AV)

A five-time First Team All-Pro and nine-time Pro Bowl selection, Webster was the anchor of the Steelers offensive line that won the back half of their four Super Bowl titles between the 1974 and 1979 seasons. Webster earned a spot on the 1970s and 1980s All-Decade Teams and earned four straight All-Pro selections between 1978 and 1981. He played 245 games in 17 seasons for the Steelers and Chiefs

Jeff Saturday (156 AV)

Saturday played 12 seasons under center for Peyton Manning with the Colts, earning two First Team All-Pro selections and five Pro Bowl nods. He spent his final season with the Packers, earning a Pro Bowl at 37. Saturday played 211 games in 14 seasons, winning a Super Bowl title in the 2006 season. 

Mick Tingelhoff (152 AV)

Tingelhoff earned five First-Team All-Pro nods from 1964 to 1969 with the Vikings, a stretch where he made six consecutive Pro Bowls. He played all 17 seasons with the Vikings, starting 240 consecutive games and never missing a start in his Hall of Fame career. 

Kevin Mawae (140 AV)

A right guard the first two years of his career, Mawae moved to center and became a Hall of Famer. He earned three First Team All-Pro selections and eight Pro Bowl nods, arguably the best center in football in the 2000s (made the All-Decade Team). 

Mawae played 241 games in 16 seasons for the Seahawks, Jets, and Titans

Tom Nalen (133 AV)

A two-time First Team All-Pro and five-time Pro Bowl selection, Nalen played all 14 of his NFL seasons with the Broncos. He played in 194 games and made four consecutive Pro Bowls from 1997 to 2000, earning two Super Bowl titles. 

Jason Kelce (132 AV)

Kelce is the only center with six First Team All-Pro selections and a Super Bowl title, earning the championship with the Eagles in the 2017 season. Only Otto (10) and Bulldog Turner (seven) have more First Team All-Pro selections at center than Kelce, who has the most First Team All-Pro selections by any player in NFL history in his 30s (six). He played 193 games in 13 seasons, all with the Eagles. 

Dermontti Dawson (120 AV)

Dawson earned six First-Team All-Pro selections and seven Pro Bowl nods in his 13 seasons, with all six All-Pro nods coming in a row from 1993 to 1998. A 1990s All-Decade Team selection, Dawson played 184 games and his entire career with the Steelers. 

Jeff Van Note (115 AV)

A six-time Pro Bowl selection with the Falcons, Van Note never was a First Team All-Pro. He played all 18 seasons with the Falcons, a span of 246 games. His last game in the NFL was at the age of 40. 

Len Hauss (113 AV)

A five-time Pro Bowl selection, Hauss also never was selected as a First Team All-Pro in his 14 seasons. He played his entire career in Washington, starting 194 out of a possible 196 games. 

Honorable mention: Dwight Stephenson (90 AV)

Stephenson is one of the greatest centers of all time, earning four consecutive First Team All-Pro selections from 1984 to 1987 and five Pro Bowls in an eight-year career. He played in just 114 games and only missed the Pro Bowl and All-Pro team once in which he started a full season.

A member of the 1980s All-Decade Team and Hall of Fame member, Stephenson retired at 30 after suffering a career-ending knee injury.