A lot of my young conceptions of sex & relationships were shaped through reading Dan Savage's Savage Love column, which is like a much dirtier and wiser Dear Abby written by a gay man, and something I distinctively remember was the theory he kicked around that many long-term relationships fell apart because one of the members was so disinterested in sex as to probably actually be asexual.
When I was an impressionable youth and everyone around me was fucking like rabbits [so it seemed], I, being the overthinking teenager I was, was tempted to place myself in such a category - but I think my libido had really not kicked in yet, and I
was[/] reading a delightfully graphic weekly column on sexytimes which possibly warped my perception of exactly how much action other people got. However, like many ideas introduced to me by that column e.g. the mutability of sexuality, asexuality as a real phenomenon is one of the things that has stuck with me since.
But, I wouldn't worry too much about whether dating age believes you or not, tbh. Asexuality is another one of those concepts people have difficulty understanding because it requires, I suppose, a measure of empathy and imagination in order to picture someone with circumstances and feelings other than your own. It's not something they're familiar with, so they don't really take it seriously.