It's right on the edge for me, like late-teens and early-twenties are off-limits as far as I'm concerned for relationships with large age disparities. There's just too much risk for it being manipulative, even if the older party doesn't intend it, it could happen by virtue of a massive imbalance of life and dating experience.

But yeah, ultimately I think a 25-year-old, in most cases has enough wits about them to understand what's going on.

Is his expectation that it won't be longterm, or is it hers? Or both?