I don't think there's a fixed period you need to wait. You certainly won't be doing your ex an injustice, especially because by moving on you're not forgetting her or burning her memory or anything. It's possible to cherish the time you had with her while looking for the next great adventure. And imagine how bad you'd feel if you knew you'd passed up on the relationship of a lifetime out of a misguided sense of honor for your ex! She's hardly spying on you to make sure you don't go on any dates for six months. The only thing that does matter is whether or not you're emotionally ready to see someone else. That's the big matzah ball. Problem is, as far as I can tell, there's no real way of knowing whether you're ready or not. The best thing to do is, if you want to go on the date (and it sounds like you do), then go enjoy yourself and see how it goes.