This mostly applies to foreign born players, but also someone like David Robinson.
In historical play, a player debuts when he is drafted - and not when he actually plays his first NBA game. Which I like! It's cool that we get Arvydas Sabonis in 1985-86 instead of 1995-1996!
The only problem with this method is that is takes his draft year age and makes it his debut year age. So all the foreign born players are actually older than they would be in that year in real life, thus retiring before they play with the guys they actually played with.
So, if I draft Dino Radja in 1989, he should debut at 22 and not 26. He was 26 IRL when he debuted in 1993.