Perfectly normal for an 18 year old girl to use late 20 and 30 something guys for sex. Relationships will be very temporary unless the age difference is 5 years or less. The data shows that it doesn't really matter if the girl is older or the guy is older.
I can relate with you. I'm at my early 20s now and I would prefer a guy who's on his late 20s. I can extend up to early 30s. In my perspective, it's hotter to think that a guy is that much older than me.
Nothing wrong with that, it means you love mature responsible guys who know how to treat a lady right. I was a teenager once and I know that guys your age can be real jerks.
And I like older women. You're good. Trust me. But sometimes older men can take advantage of a young girl. Gotta be careful. Also, you're not just dating them for money are you?