At least on my boat, age discrimination is a stretch, but I can see why some would think that. My insurance requires a liability and a medical waiver to be filled out prior to a customer boarding the boat. If there are any yes answers on the medical form, I need a signed RSTC form.
Most divers in their 70s can't honestly answer all nos on the medical form. If they can, that is great and they don't need anything extra. But most are on prescription drugs of some kind at that age and if answered honestly they would need a signoff. It isn't really age discrimination as everybody has the same requirement, it is just older divers fall into that category more often.
The online waiver is sent to them months in advance of their trips with a general warning that it is long and needs filled out prior to the trip. Most do it and we have no issues. Some ignore it and aren't happy when they can't get on the boat.