Do some girls not Orgasm?
Answers: Yes. It depends on their partner. Girls tend to be shy about unfolding their partner what they want. Maybe you're not doing it right. Ask her how she wants it.
Some girls don't catch aroused like other girls might from g-spot or clitoral stimulation.
She could enjoy a sexual dysfunction. It's harder for some women than others, and yes, it does get easier for women to orgasm as they age. Ask your girlfriend what she like. Even better would be asking her to show you how she masturbates and watching what she likes. Some girls similar to clitoral stimulation vs vaginal, some need both. Talk to her going on for what's worked before. It could also be something mental. If she's self conscious or worried (about getting pregnant, STIs, etc.) it could be much harder for her. I manifestly wouldn't write her off as someone who only can't orgasm, she just take a bit of extra work- which typically means it'll be even better when it happen! :)
I'm 20 and have have sex hundreds of times (in long-term relationships, thanks) and have never have one. It's great that you think permanent longer will somehow please her, but for me, long sessions of intercourse only hurt, and aren't going to engineer me feel anything that wasn't within for the first few thrusts. :)