The underlying worry is that, like you've said, there are a lot of inexperienced women who come out later in life, whereas many lesbians have known they were gay since their teens, so they have more experience and are less likely to want to be back in the closet. If you're older, you don't want to assume a "trainer" position (there's enough of that on okc that being bi turns off a lot of ladies who like ladies) or risk that she isn't out yet, so you have to come out twice.
I (bi myself) am also a 4 on the Kinsey scale, and find enough bi women, looking for "everyone", who don't make any mention of wanting to date a woman or in the "message me if" section only include male descriptors. It's a part of the bi stigma, but if you want to date a woman (if you're looking for casual sex, disregard), you'll need to explicitly state it on your profile.
I tend to mostly take an aggressor role on OkC as I'm only looking for women. It's been successful so far. If you've got your "looking for" set to "everyone", the assumption is that you'll be flooded with messages from men, so you have to be very forward with the women who catch your fancy on the site.
Personally, I search for people looking only for women to save time. I'm really too old to be someone's experiment (24 yes, but 80 inside). I miss out on some pretty foxy ladies (I window shop occasionally), but I've been burned enough by the heteroflexible.
My last girlfriend wouldn't have worked out on paper. She just randomly jumped on me and started kissing me during a concert but had only dated men before. We knew each other for a few months prior, were a thing for about two years (she loved me). I transferred schools, was too distant/flaky, the breakup was my fault entirely. The first "internet girl" I went on a date with (dinner + concert, she picked me up) spent an hour after the show flirting with the guys in the band. And then I swore off seeking anyone whose interest wasn't blatantly apparent. I found her on OKC a couple years later looking to "connect with a woman for the first time".
I put no couples in my profile but I get a couple a week contact me. I just find it flattering now.
If you're looking for a relationship with a gay woman, however, you'll have to understand that "bi" is less desirable than "gay" (no matter how unfair/untrue) so you'll have to be more obvious...OkC won't be on easy mode.