I honestly wouldn't worry about it too much. One day you will meet the one and you won't care whether she is older or younge, especially since you don't seem to care that much about age. I wouldn't set your sights on the age she is. Should it matter how I feel about dating older men or if I believe you should date within your age? No, all that matters in the end is that she and you love each other. As for the maturity issue, I wouldn't even worry about it. You're not the only one is more mature for your age, so it is possible you will meet someone else that is more mature also. I am also more mature for my age. I am 20 and I consistently hang out with people anywhere from a year to three years older than me. For the longest time I had hard time because I was wanting my age group to accept me, but then I realized it shouldn't matter. As long as I am happy with my friends, should it matter their age. Same for you, as long as your happy in the end, does it matter? I wouldn't worry about the odds of her being this or her being that. Don't get caught up on the little facts.
Just for fun, my answer to your original question. I see myself marrying a man closer to my age. I don't really see myself marrying a man more than 3 years older than me. But that is just personal preference.