12 is about the normal age for such sexual developement afaik
As for me, my very first urges occurred when I was 15 and then lasted for about a year.
Never really felt such urges since. I'm now possibly asexual and definitely aromantic.
I may be wrong, but it's possible that the urges were derived from a surge of hormones at that time but who knows?
Yes, I am an anomaly since everyone else at school already felt such urges at about 12 or so.
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One should also realize that I had many developmental delays (speaking, walking, puberty, growth, etc.)