It does depend on the people who are dating, but it also depends on their ages. There's a major difference between 21 and 16, for instance, but not so much of a difference between 30 and 25.
I think that, for a woman, the problem isn't just the age of the guy, but the fact that a significantly younger man isn't living the same life she is. I've dated younger guys, and had a great time with some of them, but the main problem is that they just didn't understand or agree with my priorities/responsibilities/interests and there's not really a good way to resolve that.
When I was 30 I often would date girls from 19 to 22. They were awesome and fun and hot, but ultimately still too immature.
What I learned was this... if you ( as a guy ) think it's weird that she's younger, then she'll think it's weird too.
She'll even test you when you fist meet her.
If she's enjoying your conversation, but she's a little worried about the age gap, she'll often say something like this, "Wait... how old are you?"
The best response is either of these:
"Old enough to know not to answer that question. Holy crap... wait a minute... how old are you? I never date girls older than (guess her age)!"
"I'm 33. Hey, wait a minute... how tall are you? Are you wearing heels! Oh, you cheater. I never date girls taller than 5'2"! "
The idea is to be playful and flirty. Not awkward and nervous, should she be weird about your age.
Ignore her teasing if she's mocking your age... it's her testing to see if you care. If you don't care, then neither will she. For the most part. Some girls will care no matter what, but who cares about them.
And when I was 28 I dated (I use that term loosely) a beautiful woman in her 40's. And her friends actually thought it was awesome she was dating a younger guy. I think older women really get it.