no medical examination is required, but you should have a normal physical condition. Normal vision is also needed, glasses or lenses are not a problem. You don’t have to be a trained athlete.
If you have doubts about your health or have certain points of attention (weak heart, lungs,..) then you should definitely consult with your doctor first.
A good guideline is whether you are allowed to drive a car medically. If you’re allowed to drive, you can probably allowed to fly.