Hmm. Maybe I look old. I have been on medicare since I was in my forties. I don't remember anyone specifically asking me why, but if I get a puzzled look, then I just say, "I'm on disability." That's all I say.
I wish I could work! (See my post in the grief forum.) If you truly aren't just trying to rip off the government, then there's no need to feel guilty. Besides, I did pay into the Social Security system for twenty years, so I really don't feel guilty. Just sad.