Early/late interest in sex. How old/young is too old/young?

People tell me that I’m an anamoly because I didn’t develop an interest in sex (or masturbation, making out, etc.) until my 20’s. I have a few guesses why, emphasis on guesses, but I don’t really have a concrete reasons.

It seems like what is more common is people developing interest in sex in their pre-teens or even while their ages are still in the single digits.

I tried looking this up on wikipedia but did not have any luck finding any info on this.

I’m wondering what biological and social factors (besides child molestation) influence the age when one becomes interested in sexual activities.