So you are going to determine all this how?
US airlines are governed by the Title 14 CFR addressing exit seating. But the CFR is performance oriented as to what a person seated in an exit row must be capable of performing. For example, persons prohibited from being seated in an exit row are persons who would be unable to perform one or more of the applicable functions listed :
(1) The person lacks sufficient mobility, strength, or dexterity in
both arms and hands, and both legs:
(i) To reach upward, sideways, and downward to the location of
emergency exit and exit-slide operating mechanisms;
(ii) To grasp and push, pull, turn, or otherwise manipulate those
mechanisms;
(iii) To push, shove, pull, or otherwise open emergency exits;
(iv) To lift out, hold, deposit on nearby seats, or maneuver over the
seatbacks to the next row objects the size and weight of over-wing
window exit doors.... etc etc etc
The CFR explicitly notes:
certificate holder shall make the passenger exit seating
determinations required by this paragraph in a non-discriminatory
manner consistent with the requirements....
For example, the regulation does not explicitly prohibit seating of overweight old people in an exit row. The regulation puts carriers in a difficult position of not offending paying passengers who don't look good for the possible evacuation tasks. I believe that some carriers do not allow passengers requring a seat belt extension to sit in an exit row, but that is not a Federal requiremet.