There's nothing wrong, in itself, with even a large age gap between spouses. In living memory of my own ancestry there is a couple with a 27 year gap. But I think one of the key reasons that you will not find a lot of support for something like that to become the norm is, ironically enough in our less-than-godly-West, because of the lingering effect of the ideal of Christian marriage on society. While the primary end of Marriage is the begetting and raising of children, the fact that one is limited to one spouse creates, and even requires, a certain moral expectation of parity betwixt the two.