I think when you are older, you won't think of women that way. That you are still thinking "girl" and that the gap makes a difference is from you/your past "education"/training growing up. Is your mother older than your father or is there some other couple you know like that where the relationship is an obvious problem?

I would go on the date for the experience, try not to think longer term, you've always wanted to meet/go out with an older woman, here's a chance to see what that might be like. I'd set a "lunch" date and drive to the country/water/mountains, somewhere slightly exotic and where there's a good restaurant or chance to picnic and just see how conversation and everything goes.