Michael J. Fox Says He Doesn't See Himself Living Past Age 80

Michael J. Fox says he doesn't think he's going to be around in 20 years as he continues to battle Parkinson's disease -- which is making his life more difficult by the day.

The beloved actor -- who was diagnosed with Parkinson's in 1991 -- sat down with CBS Sunday Morning for a new interview that's hard to watch ... because he says, in plain terms, he honestly doesn't think he's going to live past the age of 80 the way things are going.

Check it out ... MJF heartbreakingly describes how the disease continues to wear on his body -- which results in more accidents, falls, and injuries as he gets older. Despite this, he actually calls Parkinson's a gift ... albeit, one that keeps on taking, as he puts it.

Mike says he's fortunate to have resources around him to help him deal with it -- but notes, not many people have lived with Parkinson's for as long as he has ... over 30 years.

And yet, the guy continues to keep up an incredibly good attitude -- maintaining his sense of humor ... and carrying a positive outlook, big picture. There's a telling mantra he upholds -- with gratitude, optimism is sustainable. In other words, he says if you have something to be grateful for ... you have something to look forward to. And Fox says he's grateful for a lot.

There's a touching story he shares about watching "Back to the Future" recently on TV ... which he hadn't seen in years. As he took the movie in anew, he says his wife asked what he was doing, and he told her. He says he quipped to her, "I'm really good in it."