I think it took me about 18 months from from zero artististic / 3D knowledge to being a contract outsource artist. Then a couple years more to hit AAA.
I was utterly lucky in the beginning - a little bit over half a year since I first opened up a 3d programm to a solid job that actually paid my bills (but it was a small studio, supported by a Casino app developer so don't take this as sign of me being good). I left the studio after two years to actually make some progress…