Obviously there are exceptions and it can be totally unpredictable, but I think male pattern baldness does slow down with age, or can start and progress very slowly in older men. My dad was a Norwood1.5/2 until nearly 40 and is now Norwood 4ish at 67.
Nixon seemed to have had recession to around Norwood 3 territory probably in his forties and then it seems to have stayed there, albeit getting thinner as he got older.
I was thinking that yesterday about some classic actors like Lee Marvin, Gary Cooper and George C Scott. These guys were strong NW3's by 30 yet barely lost anymore into their old age, still keeping thick hair despite having no temple hair. Same with writers like Hemingway, Bukowski.
It's quite common for men of that era to bald like that (same with my grandad) yet it's rare to see it in post-boomer generations. I hardly ever see guys with NW3 who don't eventually thin or develop that balding 'island'.
Makes me wonder if there's a contributing factor from our modern lifestyles that makes it more common to bald in a more aggressive/progressive pattern.