I would not date her because I'd know that developmentally I SHOULD be at a very different place than this chick and the fact that I'm not, and can see myself dating her is a problem. A problem that isn't hers, but mine. And so I would push myself to make the 36 year old decision even though my immediate impulse would be date this hot youngin'.
That said, your question is not about me, but some 30+ dude in your life. Having been 18 and now being 30+ I assure you the 30+ guy that wants to date you is bad news. Either he knows it or he does not. Irrelevant. Dating an 18 year-old is not like dating someone 25 or even, even 21. Being 18 is like being 17 with a birthday coming up. It's super young. I wish you'd have asked me, if I were YOU what would I do. That answer would be: Keep swimming. There are plenty of contemporary fish in your sea.