There seem to be a couple of stages of life, although there can be circles that cross more than one. Maybe
1) intra college, with it probably being a good idea to get settled down as a freshman first, keeping the age close in
2) post college up through 25 - somehow there's a lot of getting used to life past college there (though kids can make you grow up a lot faster if you have them) - the workable age range expands a bit during this phase
3) late 20s through mid thirties range - ...
?
and beyond there I don't even have a guess - I haven't been that old yet. A lot of this has to do with priorities - first college, then the first job and settling in, and then getting set up in career.
And yet in all of this, the exceptions would seem to be where the two share some common interest they can share as equals and where their values and priorities come out the same - there can be no partnership without common ground and common goals.
For example, I asked my mom a few years ago what I was like when I was younger (not that I was ready to marry then) . Her reply? Shorter. I was concerned about responsibility as a child (though I still watch saturday morning cartoons - no, I'm not a big kid). Who I am has stayed fundamentally the same, and that echoes in other people. I would probably sync with someone that had some of the same fundamental qualities, even if they were younger, as I always hung out with older folks.
Perhaps it's the idea that when you find someone who may be it, there's a recognition that who they are is on the same basis of who you are - a connection?
-kc
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(Just don't connect _too_ easily on just anything - over the years it takes work to stay connected and to build new connections - one of the fundamental qualities no matter what needs to be commitment not just to a dream, but to making the relationship that God has given work, no matter the cost).