I work in an airline, and people over 70 have to issue health certificates to prove that they are fit to ride. The general content is whether you have severe hypertension or heart disease, whether you have had surgery in the last month, and whether you have an open wound. That's about it. When you check in, you need to show this certificate to the manager on duty on the ground. If everything is all right, there is no problem for the old man to fly. You'd better also give some airsickness stickers to the elderly to prevent them from airsickness.
Also, if there is a problem, you still have to fly, and the airline will sign a waiver for you. If there is a problem on the plane, it has nothing to do with the airline.
The booking procedure for the elderly is the same. Please indicate the age of the elderly when booking tickets. When you check in at the airport, you can ask the staff for a seat in the front row to take care of the elderly.