My best friend (at the time, he turned out to be a jerk) came out as ace when we were both sixteen or so. So I started looking into being ace. I was only looking into it for the purposes of being a good ally, at the time I was pretty sure I was a lesbian. However, when about a year passed, and I felt no sexual attraction to anyone, I realized I might be ace too. I started saying I was questioning at seventeen, and I came out as ace at eighteen (after some sexual experimentation with my at-the-time girlfriend).
Figuring out that I'm lith/aro has been a lot harder. I really only figured it out right before I went off to college. I was basically sitting down in Spanish class one day, and thought, "everyone I've ever crushed on, I've only ever wanted to be friends with them". This was a revelation to me. I then realized I could fit in very nicely with either the lith or aro category. I pretty much considered the matter settled after that. I did meet someone online after my first semester of college, and fell in love with him, but I still didn't want a romantic relationship per say (I wanted a QPR) so I feel that doesn't invalidate my identity.
I am out to my Mom. I am not sure if she believes me or not (I'm autistic, so sometimes it can be hard for me to parse these things). I am also out to my stepdad. I think his main worry is that I'm going to be lonely forever and never experience love. That is a legit concern (I haven't told him that), because I spend a lot of time alone, even in college. But I have a really, really good crop of online friends (including one who calls me "Mom"). So, I am not worried about that for now.
Hope that helped.
---Alto