For me it was about 6-8 years old. Ofc I had no clue what being gay or sex was, but I was very much attracted by boys at that age, and specially, when I saw very muscular men, it made something tingle inside me.
EVEN GAYER SHIT
By 13 I was already drawing big muscular men, and making huge play-doh penises to my He-man action figures.
DISCLAIMER (in case someone is wondering) No, I have never been sexually abused or anything of the sort.