I can totally relate to that. It's usually never been guys around my age who tried to talk to me, but guys old enough to be my Dad or Grandpa (no thanks!!) The crazy thing is, when I was 17 and a 40-year-old tried to talk to me, it was like, yuck. And now if a 40-year-old tries to talk to me, I have to remember, "Oh shoot, that's in my age bracket now!!!"
I'm guessing you're a level-headed, mature person? A lot of older guys are attracted to younger women as it is (I think that some see it as a "second chance at youth", especially, for instance, if they were rejected in high school--many seem to think now they can attract the young pretty girls who never seemed to talk to them when they were younger--just a personal theory, and a younger woman (in age) who is responsible and easy to talk to is all the more alluring to them.
Has anyone else out there also found that older guys (at least in my case) seem to think they can "buy" you? I mean, they'll tell you what they could get for you or give you... I know a man is to provide for his household, but this is in more of a "I can impress her with my status in life and my wallet"-type vibe. I am not saying that all men are like this at all but I do believe that many men seem to think of women as just expensive toys that can be bought as long a they have enough cash (we have the strip clubs to thank for a lot of this mentality, I think.)
Just a few years ago, I had a guy old enough to be my Grandpa try to tell me where I work, "I could buy you jewels and cars..." I looked at him and said, "Sir, as you can see, I have a job. Anything I want or need, I can buy myself."
In my case, I think guys like that try to talk to me because they assume I'm foreign, don't speak English well, and am naive enough to be impressed by their pseudo-macho facade... And, everyone has their own taste. I have a good friend who, all her life, has been attracted to guys 10 and 20 years older but oddly enough, she wound up marrying a guy who is about 2 years younger.
Anyway, stand your ground, and best wishes!