Depends on where/how they played. I'd argue that anyone who played travel hockey and varsity high school, can likely play B, if they're still in shape. Once I'm back in better shape, I fully plan on stepping onto our B roster. I'm still not in that kind of shape right now, despite having dropped like 25lbs over the past year or so.
Most guys are C, IMO. Even in the C2 leagues there are usually a decent amount of good players on each team. A teams are generally guys who played some level of juniors, pro, semi-pro, or college, and are mostly still in that kind of shape.
DHF is talking men's league levels.
Amateur travel hockey is A, AA, AAA, and then either high school or juniors, then college. College has different levels, obviously, like D1, D2, Club, etc.