at about age 10 in the early 1970s, I took a rafting trip with my family down, I think, the American River in the foothills of the Sierras in California....at the boat-loading area near a bridge over the river, two in-shape guys in their early 20s, I presume, got naked and went skinny-dipping for a bit to cool off.....I think (??) it was the first time I'd seen naked adult guys (except for Dad) and I remember being fairly entranced at how built and good-looking they were.....
later, at about age 12, I remember a dude one grade ahead of me in the locker room who had evidently already gone thru puberty....we weren't required to take showers, but he usually did and was possibly proud of the fact he'd already matured a bit: he'd linger naked just a few seconds too long at the shower exit in full view of all....well-hung and good-looking.....