He was diagnosed at 21 and given three years to live
Before Hawking even started discovering mind-bending scientificy science stuff (that’s a scientific term), he was already defying it! See, when Hawking was only 21, he was diagnosed with Amyotrophic Lateral Sclerosis (AKA Lou Gehrig’s Disease, AKA Why Everyone Dumped Ice Water On Their Heads That One Time), and doctors told he only had three years to live.
Hawking, upon hearing the news, promptly took one look at Death and said, “Nah, I’m good,” and proceeded to live until the ripe old age of he’s still alive. The guy who was supposed to croak at 21 is still going at the age of seventy-four! While we’re not mathematicians, we calculate that to be roughly a bunch more years than the doctors gave him. This must make his current doctor super-nervous when saying anything to the man during his annual physical.