I'd say 5-8 years or even longer is still a newbie
..we know some, but we are always learning more. We/I are always learning how to improve the diet, the exercise, the routine. Your body is always changing, and trying to keep up with it isn't easy. When bulking/cutting/ or just maintaining, the diet is always fluctuating, the routines and exercises may vary. I don't see it as a newbie or expert because I'm learning stuff or researching ideas/supplements/routines all the time.
When I get to the point where there is no more to learn, then I will say I'm not a newbie
..just my view on the subject.