How are they still here? How are they still this good?
Steve Nash and Kevin Garnett have shown few signs of game-erosion, despite being nearly as old as James Naismith. Nash plays a young man's position at age 38. The most popular Fox show in Garnett's rookie year was Married with Children. Another favorite "KG's old" fact: He played in an All-Star game with Joe Dumars.
Yet here we are, fresh off Steve posting a career-best field-goal percentage last season, and fresh off Kevin Garnett deserving a DPOY that was given to Tyson Chandler. We've been waiting for both players to crumble like a Jenga set for a half decade. Now, I'm so resigned to the idea of their basketball immortality that my team predictions don't even price in the possibility of a collapse.
So who wins a longevity battle between these two? Since I'm not a doctor, or a psychic, I'll base this guess work on what I've seen from their games.
He has become the best long-two artist among big men. This skill should hold up, so long as Kevin Garnett has hands and feet. If KG challenges you to a game of H-O-R-S-E 10 years from now, I don't care if he's ballooned to 300 lbs. Don't do it. As Kenny Smith once said on Inside the NBA: "Your jumper is like a great woman that never leaves you. Your legs are like those girls in the club...they leave."
The most surprising aspect of KG's latter career has been his unwavering defense. Older players tend to defend better, and Garnett has superior length to leverage. Expect a drop-off in Garnett's pick-and-roll mobility, but also expect him to remain an important defender. Considering that Dikembe Mutombo played to age 42, I could see KG going well past 40.
Also working in KG's favor: He's quite motivated by people thinking he's old in the first place:
KG's signs of decline are subtle. His rebound rate has declined, dipping to a still respectable 10.6 from a 14.2 in 2004-2005. And, last season, he attempted a career low near-rim tries (via HoopData), with only 2.7 per game. So long as Garnett keeps hitting shots at 16-23 feet at 48 percent, he can withstand losing a lot more of those rim attempts.
Just like KG, Nash's longevity is based on his jumper. He's a historically great passer, but Steve may well be the greatest shooter of all time with four 50%-40%-90% (FG%-3PT%-FT%) seasons to his name. The aforementioned passing ability doesn't hurt either, as it's a skill that tends to accompany a man through his later years.
John Stockton would be the Nash model, as he played to age 40, and was still damned good at 40. Nash is a better shooter than Stockton, possibly a worse passer, and might lose the longevity battle on account of back injuries. Stay tuned.
I do see storm clouds on the horizon for Nash, though. Last season, he scored less while accruing a career-high turnover rate. Subjectively, I saw Nash struggle on pick-and-roll traps. Where he once was able to elude a double-team, recent Steve would often get swallowed up by the blitz. As for his defense...let's just say he's lucky to play a less-than-vital defensive position.
In the end, despite Kevin Garnett's 2008-2009 knee injury, I expect a longer career from the big man. His position relies less on speed, and he's never going to lose his height. Both would be decent bets to play past 40 and beyond—a staggering feat in today's NBA.