Virgin-Whore complex. It's standard guy psychology -- males tend to develop this virgin-whore complex about sex. We want her to have been virginal before us, but be a freak in the sack WITH us. Not gonna happen.
If a grown woman in her thirties wants to sleep around, more power to her. OP already stated he wants to sleep with her. But you have to pick -- either you live in a world where girls will have sex with you on the first date (awesome, right?), or in a world where you don't get to have sex with her. But if a woman happens to be open to sex, which you want, and you want to pursue that, then you lose the right to call her a slut.
If OP wants to date her, great. But don't take advantage of her willingness to have sex, then call her a slut for it. For god's sake, man, havbr some consistency.
Everyone owns their actions, btw. You wanna sleep around, you risk the diseases. And looking clean ain't being clean.
Still, every man should, at some point in his youth, date the girl his mother warned him about. 🙂