Having worked in health care for decades (a large,well known hospital) I can guarantee that there are many,many people...of *all* ages....with serious.long term (if not permanent) disabilities.
Of course there are frauds....many frauds.Crooked doctors (particularly chiropractors and psychologists),crooked lawyers,crooked patients.I've seen them.But my guess is that 75% is high.In fact I'd guess that even 50% is high.
You have worked in an environment where you would see a concentration of the legitimately disabled.
Your run of the mill Freeper is out in the general population and probably has a better sense of the legitimate to fraudulent ratio.