There are none..
There is no weight and height requirement. So long as your feet can touch the pedals, and you can see over the steering wheel. A government agency? That would qualify you as falling under the disabilty act, if your feet won't touch the pedals, or you can't see over the wheel. You might be able to sit on a phone book, and strap some blocks to your shoes. The weight? As long as you can pull yourself up into the tractor, you'll be fine. Hearing? I'm 25% deaf in one ear, and I passed. Very seldom do you get a hearing test on a DOT physical.