Certainly, severe physical limitations would be considered as a disqualifier for military service. Additionally, mental disabilities would also be a possibility for disqualification.
There are several different permanent disqualifiers for not just the Army, but for any branch of service. Some of the disqualifiers may be bone deformities, missing limbs, or heart conditions.
Yes, there are. You will not qualify for the army if you are permanently disabled -- the blind, deaf, paralyzed and mentally disabled will not get in. You will not qualify if you are too old.