Assuming his body holds up, I don't think he will have the motivation to go to even 35.
Apparently, he's known to be slow starter, not putting out in Nov and Dec.
Now he's seems so bored and weary during the season, fed up with refs, not hustling, not really enjoying himself very much, 3 years in a row with injuries, biding his time with the pain-in-the-ass season until the playoffs start.
One could say he's kinda burned out. Being set for life financially and his limited athleticism waning visibily, the only thing his career is missing compared to the very top players is the very difficult B2B Chamiponships. If the Spurs win 07 and 08, Tim could be gone, retiring like David did, with a Championship.