I had a relationship with a large age gap when I was your age. I feel like I sort of lost out on something, as the person I was with was in a totally different place in their life than I was. I lost out on really being in and experiencing my 20s.
But if you're 18 and trying to get pregnant, it sounds like you're already willing to skip that. I'm not judging you for it, not at all! Just be aware of what you're giving up.