How did you realize you were ace?

I have a question fellow aces! Particularly male asexuals.

How did you realize you were asexual? I'm asking for a male perspective because I want to write a male asexual character. I would just like to know if there's a difference with the female asexual experience. Female and NB peers are free to reply as well so I get a more holistic view of the diversity in experience!

Thank you in advance!