So what exactly was he playing at? The fact that he marries a girl closer to his age, surely shows that he doesn't have a preference for older women...
I think the fact that he married someone closer to his age may have been due to any number of reasons:
Either one or both of them deemed their relationship a little out of the ordinary - marriage may have been socially unacceptable/impractical etc. Perhaps Ann may have been unable to have children due to her age (or other reasons) hence they didn't marry. Isn't/wasn't procreation one of the main reasons for, or expect from, a marriage?. We don't know her status. Ann may have died or married someone else.
Maybe Nathaniel thought Sarah a more suitable partner for marriage - it may not have been a conscious decison to choose a younger partner. I think age was probably irrelevant to him. However I can see Nathaniel doing the 'right' or 'conventional thing' in most aspects of his life, so it was probablay the case when it came to his choice of a marriage partner.
I like that fact that his relationship with Ann is unconventional. And I like to
think that he
did have a penchant for older women.
Just my thoughts ....
