I think you don't deserve the downvoting you are getting even though the timing of your question is not great, you're still trying to understand what the natural progression of ALS is.
I actually had no idea he was that old. Maybe he looked younger than he was because he had no wrinkles.
For a lot of people that die natural deaths they could have lived longer if they had kept fit. It just gets really hard to either do or justify when everything hurts and gets harder to do year over year. Or when you are confined to a wheelchair since your early 20s, were told you would only live two years, and then beat that prognosis 27 times over.
But if you are able, even small amounts of cardio exercise could dramatically extend your health and lifespans in old age.
But after a certain point, that cause of death starts looking pretty meaningless. Everything is failing at once; if you hadn't died of your actual cause of death, you would have died shortly afterwards from another one. In that sense, you do "just die" of old age.
That said, his original prognosis was that he wouldn't reach his 25th birthday, so he hasn't really done too bad.