A big part of this question is how many elite years you think Lebron has left. He's already accumulated over 42k minutes at 30 years old. It's likely that he hits 50k minutes before his 33rd birthday. That's more minutes than Michael played in his career.
Probably a few. Unless his body just breaks down, he should age pretty well after he stops being tops in NBA and still be top 10-15 for little bit similar to Tim Duncan. Even if his athleticism declines, he still has the size/skill combo.
The fact he is on a good team and in the far inferior conference should help him age better.
43k minutes at age 30 is staggering though. Nobody even comes close to that. Kobe is probably 2nd and even he didn't really play until his 3rd year (50 game lockout season), had 3 years in the middle of his prime where he didn't getout of rd 1, missed more time due to injuries, consistently had better teammates, etc