Actually it was in the mid 70s when he was about 45. Maybe it was 84 Lumber, I don’t remember. He developed Alzheimers in his mid 60s.
Precursor symptoms may occur as early as the mid 40’s and often get confused and passed off as “those subtle declines” that begin occuring in ones life anyway.
It doesn’t surprise me that he developed alzheimers...which when I read your posting I was prompted to ask about his developing dementia. Hopefully you do see that some of your marriage issues may have had something to do with the mental storm he had been dealing with for decades while not exactly being entirely conscious of what was happening to him.
I also feel for you as it must have been frustrating for you in dealing with those sudden illogical twists and increasing quirkiness of his personality and lapses of judgment and memory with any angry emotionality that went with all that.