You would be surprised at how often 22 year old girls will hit on men over 40. Especially with a couple of beers involved.
The most common reason that would happen is the guy over 40 has money the 22 year old girl wants to get her hands on.
Honestly, if you're a guy over 40 or so, you need to be aware that most young women aren't going to find you physically attractive like they may have when you were younger, so if one is coming on to you, then you have to ask yourself why. If you happen to have (or appear to have) a decent or great amount of money, that's probably the answer: The girl is effectively prostituting herself to you in exchange for the chance to get at your money or at least get you to buy things for her.
It's a difficult cross to bear. Women are hard to figure out. They get all dressed up, prop their cleavage out and then seem to be offended if they catch someone staring at it. Go figure.
I do agree with this to an extent. You can wear what you want, but you should expect people to look at you when you wear certain things, and really don't have the right to be offended when they do.