Guy my age at my church had it years ago. He was diagnosed in his mid-30s. He passed away in his mid-30s.
The worst part about it is the person is still completely aware of everything that is going on. So you are essentially a prisoner in your own body. Clearly not making light of other diseases as my brother passed away from a 14yr battle with cancer at 43, but up until the last couple of years, he was at least able, although in some cases labored (because of treatments and surgeries), to get around and really up until the last month-and-a-half before he was put in hospice, communicate.
Within 6 months of his diagnosis, you could barely understand him when he talked. A few months after that, he became bed-ridden until he passed away. I think it was about a 2-3 year ordeal.
Terrible is an understatement when describing ALS.