I care little for age and everything for maturity. Someone's apparent age is more important than their chronological age (except, of course, in cases of age-of-consent laws. I wouldn't get mixed up with a 17-year-old girl in California, for example, no matter how mature she was, and I wouldn't recommend it to anyone else in that state.)
I'm 32. But I'm also a college student and therefore most of my friends are quite a bit younger than I am. If I met a fellow second-year accounting major and future CPA who just happened to have graduated from high school in 2008 rather than 1995 (which would make her 19 or 20), would that deter me? Hell no! We'd be at the same stage of our lives (yay misspent Gen-X slacker youth!) and at the same stage when it comes to stuff like goal achievement and future plans. The 13-year age difference would have no bearing at all on the nature of the relationship (except for me having a lot more life experience, but that's not necessarily a bad thing either.)
Steering this back on-topic, I'd say that 17-year-old in the original post scenario should not be touched by anyone much older than she is, only because she's 17 going on 13 emotionally. That girl needs to grow up, and any guy dumb enough to get mixed up with her is in for a world of stupid teenage drama (and most college-aged guys I know are only after one thing from a girl like that...and rightly so.)