I'd much rather have a 93-year-old named Jack LaLanne in the exit row than many people in their 40s or 50s.

If you want to qualify passengers for exit row seating, have demo stations where passengers can demonstrate ability to open the exit door and exit the airplane quickly. Gate agents can mark their frequent flyer accounts with the date of passing such a test so that passengers will only have to retake the test perhaps once every five years.

As a bonus, the demo stations, made with real old airplane seats and overhead bins, can be used as carryon sizers (and customer of size sizers).