Another early remembrance in conjunction with this topic: boys summer camp in 1958, my second annual, when I was 9. Our cabin of 15 boys and 1 college-age counselor, along with another cabin of boys the same age, went on an overnight hike into the woods.
Very primitive, almost Outward Bound in style. We had no tents or sleeping bags, just a single wool blanket for each of us to spread on the ground. Brought out by a rickety stake truck, along with hot dogs the 2 counselors taught us how to cook on an improvised campfire as our supper.
About midday we went "exploring" (exploring exactly what besides more heavy woods I never discovered). We did come across a shallow mountain stream, and it was agreed we'd take a swim. We had brought no clothes with us other than what we wore, so we skinny-dipped, common for boys in the 1950s. Our counselors, too.
Some of us, like me, had never seen a fully naked adult male before. There were exclamations from the boys that "He's got hair on his thing!" and similar. I found myself enjoying the sight. Not of the other naked boys, nothing new to me, but of how grown men looked, with all their hair and size.
At one point the other counselor got a hardon. Why I can't say, maybe the shock of the cold water, or the air coming out, perhaps the boys still calling attention to his stuff. My own counselor was laughing hysterically, and told him to get back into the water and swim it off.
I presume most of us had never seen a boner before, I know I hadn't. I don't recall having had one myself to that point, I think that was a year or 2 away. I didn't know a dick could manage that trick! I was incredibly naive.
And each of the 3 summers I attended camp I thought my cabin counselor, a different one each year, was so good looking. Well, so were the other ones in the camp, too.
Therefore I'd add summer camp counselors to my list of males to whom I was attracted at any early stage. In a way I didn't understand at the time, and wasn't able to comprehend for many more years.