I have yet to come across a game that really simulates Feudalism per se. I really wish something would get made in this area. If you were to be content with some element and not others then all of the following will cover and detail some portion of the middle ages:

Kingmaker (Avalon Hill)
Blood Royale (Games Workshop)
Empires of the Middle Ages (SPI)
Holy Roman Empire (Issue 33 of the Wargamer)

Unfortunately all of these are out of print. You should still be able to pick up a copy of Kingmaker at a store or off the net without too much trouble. The rest will require scanning for auctions and then paying a good wad of money to win them.

As far as the age group is concerned I'd think that Blood Royale would be the best. The games covers trading and warfare across Europe in the middle ages but the core of the game is building up and maintaining dynastic families through the years. If you were to hack the rules up a bit and streamline the record keeping then it would be an interesting simulation of how politics were governed by family ties.