I think the problems are twofold:
Lack of historical female characters: This should be fixed by generating a bunch of random female nobles at the start of the game. In particular if a man has an heir then it seems reasonable to assume that he has a wife. Assign her to a random noble family in the game.
The 16 year old virgin: The way it's set up now pretty much everyone gets married at 16 and everyone gets married right after their spouse dies. Game mechanics push you if you don't. That doesn't make much sense, there should be some incentives to play the field, marriage wise.
As I understood it, the problem appear sin later game, too? Hence, it is a problem of the instant marrying?