Wow, assume much?
My health is not perfect. I have 4 perscriptions for my allergies/asthma alone. Not to mention arthritis, and other assorted goodies. However, as I have been dealing with those conditions for a while, I have a good idea how much I can push myself. And I know that if I try and do too much, or am unfortunate enough to stand downwind of the fireworks, that I am going to have to deal with the fallout from those bad decisions.
Even so, I know that sometimes I can make all the right decisions and suddenly have a bad day. And I would be upset to have to miss a meal and pay a service fee. However, those times are the exception, and not the norm. Odds are if book and ADR, and make the right decisions concerning my health, I will be able to enjoy my meal. I would think most people who deal with cronic or severe conditions have the same awareness, and also the same understanding that even if they do everything right, sometimes crap happens and you have to miss out. Still, I think those times in most instances are not as common as people are trying to make out.
I also think my 70+ dad knows how far he can push himself at WDW too. Being older does not mean you are suddenly so frail that you stand a good chance of missing your ADR. Being older is not an illness.
No matter who you are, it comes down to being comfortable with a small chance that you may lose what, in the large scheme of a Disney vacation, is a small penalty.
If you are not comfortable with the risk, then choose to book at one of the many restaurants that still don't charge the fee. It is pretty simple.