A steadicam is a heavy rig, and is not known to be the easiest thing to operate. The weight alone is something to get used to and moving is a challenge (think dancing the waltz with a 45 lb weight attached to you).
Strength and endurance are a big help if you want to operate. The better condition you are in, the better you'll operate the rig.
Other good things you'll need:
- No back problems
- No problems with dizziness or disorientation
- Good eyesight.
- A working knowledge of the film and/or video industries.
Also prior experience on a film set will help as well as good connections with your mentors, as they will likely hook you up with your first job.