Last year, I wrote about how rare and impressive it was to see Ray Lewis and London Fletcher still playing at high levels. Lewis did not have a great 2012 season, but managed to walk away from the game as a defending Super Bowl champ. Fletcher was even better, and was named a second-team All-Pro by the Associated Press.

Pro-Football-Reference.com’s Approximate Value system goes back to 1950. Only five times since then has an inside linebacker recorded 10 points of AV at age 36 or older: London Fletcher and Sam Mills are each responsible for two of them, with Bill Pellington (’64 Colts) rounding out the group.

Fletcher has never missed a game in his career, a remarkable accomplishment for the 15-year veteran. Consider that only three linebackers have appeared in more games than Fletcher (240): Bill Romanowski (243), Junior Seau (268), and Clay Matthews, Jr. (278). And all three of those players were outside linebackers, giving Fletcher more games than any inside linebacker in NFL history.

Which is pretty incredible for a player who received no awards or postseason recognition until turning 34. If all you knew about Fletcher was his performance from age 34+, you would assume he was a first ballot Hall of Famer. In 2009, he made his first Pro Bowl, and Fletcher was sent again in 2010 and 2011. The last two years, he’s been a second-team All-Pro, giving him some recognition in each of the last four years. Fletcher is on the short list (with Mills and Lewis) for the title of most successful inside linebacker from age 34+.

On the opposite end of the spectrum is Patrick Willis, who has now made the Pro Bowl in each of his first six seasons. The only other defensive players to do that: Derrick Thomas, Lawrence Taylor, Joe Greene, Dick Butkus, and Merlin Olsen. That’s mighty fine company, but it’s hard to find any flaws in Willis’ game. Not a fan of Pro Bowls? Since 1970, Lawrence Taylor, Reggie White, and Willis are the only defensive players with five first-team All-Pro honors in their first six seasons.

Willis has played well on bad defenses (2007, 2008) and on exceptional defenses (2011, 2012). He’s actually tied with Ray Lewis for 6th in most AV accumulated through six years. They both trail only Alan Page, Taylor, White, Jack Ham, and Herb Adderley.

Willis has shown no signs of slowing down, but expecting a Fletcher-like tail end of his career is probably unrealistic. This time three years ago, Willis was being mentioned with Jon Beason and DeMeco Ryans as the game’s next group of great linebackers. Generally, inside linebackers have some of the shortest shelf lives, as the physical component of their roles leads to very short careers. It will be interesting to see how long Willis can last, and it’s always worth a minute to step back and appreciate how unique the accomplishments of Willis — and Fletcher — truly are.