I still don't know why this is expected of men, but I guess it's just one of those cultural things that I'll never understand. I certainly wouldn't link it to "gentlemanly" behavior, since I think this outdated standard still leads to a lot of male expectations that are anything but gentlemanly.

Could we find a better solution? Offer to pay the meal but allow your date to get the tip, or something? So it can feel less like a 1950s flashback and more like a meeting of equals?