How short is too short for a skirt on a first date?

I have a first date coming up and I have a really pretty outfit picked out except that I'm wondering whether the skirt is too short or I'm just paranoid. It's a black skirt with ruffles that comes about halfway between my knees and my crotch. Everything else is fine, the top doesn't show cleavage and it's not too tight or anything like that. If I don't wear heels with the skirt, it doesn't look short but when I put heels on (which I plan to wear) it suddenly makes it look short. I'm only worried because I know that this man is looking for a classy woman and if I'm not dressed tastefully it might turn him off. And he's 40, so it's not like he's some teenage guy who will drool over anything. What do you think?