I was around 12 when I read Azazel by Isaac Asimov. It's a series of short stories about a mischievous demon. As I recall there are two amazons in it: one story has a tall muscular woman with a fiery temper from a family that crushes cars with their bare hands, and another has a tall woman who breaks men when she drinks. Neither were particularly flattering to the women, but they grabbed my interest so much I remember them 25 years later. Not too much later I read "We Are All Superheroes" in Science Fiction Age magazine, which has a horny muscular superwoman, treated more sympathetically. It was a few years later when I was maybe 15 that I discovered actual female bodybuilders thanks to Al Gore and the internet. I don't know who it was, but one image that particularly captivated me in my teens was a back shot of a very dry, muscular bodybuilder with big striated glutes that popped out of her butt and looked like handlebars I wanted to grab onto and worship. I've been hooked ever since.

25 saw pictures of Cory and that was it

Siskel and Ebert showed a clip from 'Skin Deep' of Raye Holitt posing. "How do you feel about that!" I was hooked after that.

Siskel and Ebert showed a clip from 'Skin Deep' of Raye Holitt posing. "How do you feel about that!" I was hooked after that.

 Similar for me also . When i first saw American Gladiators with Raye , and the others . Then when i saw Laura Creavalle posing on espn i was 100% hooked

when i was a kid, less than 10 for sure
was attracted to wonder woman, bionic woman and other tv shows where the female was so strong

then saw a female bodybuilder on a magazine for the first time, and my life changed forever

Between 10 and 15... (actually when I started "individual" sexual activity!)
I was captivated by two ladies, both older than me: one living in the flat opposite mine, and I could not take my eyes off her when she cleaned her windows, holding the frame with one arm and scrubing the glass  with the other hand; the other one with big calves I used to follow on my way to school, especially on the stairs when leaving the underground; I said hello to her once, but she did not reply.
Later on, I met my wife, a swimmer with strong muscles...