Through the 2011-12 NBA season, only 17 players in NBA history have played past the age of 40. Recent NBA free-agent signings have ensured that this number will see a big spike.
Jason Kidd (Knicks), Steve Nash (Lakers) and Marcus Camby (Knicks) will be over 40 when their new multi-year contracts expire.
Tim Duncan (Spurs) and Kevin Garnett (Celtics) will be near 39 years old when their recently agreed upon deals come to a close.
These players' productivity will probably decline to some extent. However, as past NBA stars have proven, they can still make extremely high-quality contributions to their teams even at very late stages in their careers.