I think he's right on the 90's.......the 1st EVO was '84 and I don't think they started becoming 'fashionable' until the more dependable motors brought in the $$$ people.
Back in the late 70's there was a flea market - auction that took over the old Two Guys and Great Eastern store (who remembers those two!).
One of the biggest hits at the flea market was a "leather shop".
My local dealer at the time (and in retrospect, one that I could have been an eventual principal) got the idea to move some bikes around (opened up the second floor) and brought in a bunch of t-shirts - leathers and all the other stuff "kids" were wearing at the time.
Got to the point you had to push your way through the kids and leather hunters to get to the bikes.
I remember the time frame well, it was when I bought my "special" 82 Lowrider (had the badge on the front fender) and my brother bought an 83 (I think) Lowrider (his had the twin belts like the Sturgis, my all time favorite) So it had to be around the 1982 model year. My bike and my brother's bike were stuffed all the way in the back of the store.
Interesting side story - both my brother and I bought our bikes around the same time, didn't know each other was looking and we each ended up not buying the color we really wanted because there was a hold on it!
I wanted the red bike with the twin belts, he wanted the black bike with the fender badge. We were going to just ride up and surprise each other.
We both ended up at the dealer on the same day, within an hour of each other and picked up the bikes, what a surprise to each of us.
Memory check here -"Two Guys from

?"
more dependable motors
Spy, my 82 Lowrider was the best bike I have ever owned, and I miss it.
50,000 plus miles and all I ever did to it was maintenance and tires (not including an upgrade or two).