When I was 19, I was working full-time and overtime, building a career, taking care of myself and my parents, paying ALL the bills, and also taking classes at a university. There are many 30-year-olds who don’t experience responsibility like that, nor do they have the maturity level for it.
Sure, it’s concerning. I’m worried for girls like that, because older men often seek them because of their lack of experience and boundaries. Not to mention, some men have bruised egos and they seriously think that getting a young girl means they still “got it”. If that’s the case and your friend is an emotionally abusive manipulator - sure, you’re right, someone needs to save the girl.
But the best case scenario, the girl is just having fun and she’ll move on to a new guy pretty soon. Or maybe you’re completely wrong and they are actually in love and will end up getting married and having a loving family. There are many different scenarios, you know.