Tim Duncan has been Hall of Fame-bound for some time, but his legacy beyond the five championship rings and repeated 50-win seasons is also his longevity – a sustained run of success aided by his coach's desire to preserve him by providing ample rest, his own dedication to fitness and a willingness to subjugate his game so that others could flourish.

At 39, Duncan is the second-oldest player in the NBA – a mere 37 days younger than the league's eldest graybeard, Andre Miller – and will soon become one of only two dozen players to extend their careers into age 40. Yet Duncan remains a productive, starting contributor for a San Antonio Spurs team that has been contending for titles since he was drafted first overall in 1997. And to Duncan, the secret to remaining relevant in his 19th season comes down to something that neither he – nor Coach Gregg Popovich – could control.

View photos In his 19th season, Tim Duncan, 39, is still getting it done. (Getty) More

"A lot of luck, honestly," Duncan told Yahoo Sports. "Same coach. Same organization. And just lucky to stay healthy."

Duncan's good fortune has allowed him to delay Father Time's inevitable knockout and outlast every other member of his draft class. The ability to consistently have a prominent role on a team destined to play meaningful games despite his advancing age has helped Duncan stand out among peers, rivals and fellow future Hall of Famers Kevin Garnett and Kobe Bryant. Garnett, just 24 days younger than Duncan, is mostly a foul-mouthed mentor, passing along wisdom and four-letter encouragement to the young pups in Minnesota. Bryant, 37, is struggling to carry the Los Angeles Lakers as he once did, and now just walking to his car after games has become a chore.

Dallas has attempted to replicate what the Spurs have have done by finding a supporting cast to relieve the burden on 37-year-old Dirk Nowitzki. But the Mavericks haven't won a playoff series since winning the title in 2011.

Other remaining players born in the 1970s are mostly holding on in reserve roles.

Growing old in the NBA is never fun and the transformation is now being felt in the next generation, as perennial All-Stars of the legendary draft class of 2003 have entered the stage of their careers when they have to adapt.

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This season, one of the league's best-kept secrets became evident when LeBron James was forced to have a second round of back injections, exposing the vulnerability of even the game's most physically imposing player. James, in his 13th season, has been diligent in protecting his back, doing pregame workouts on a stability ball, stretching and wearing heat packs while resting on the bench.

Dwyane Wade doesn't feel it is a coincidence that James's routine has become more intense now that his former teammate is approaching his 31st birthday.

"It’s the other side," Wade, 33, said of turning 30. "LeBron’s body has taken a beating. It’s just about adjusting your game and your body. Some nights it’s going to feel amazing; some nights, it’s not going to feel as good.

"You feel different when you turn 30," he said. "It’s like the day you turn 30, you wake up that next day and you’re like, ‘I feel different.’ In this league, it’s all about being able to adjust your game around how your body is feeling."

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