POLE7645: Congratulation. You should be proud.
I didn't finish a game until I got 12 at least (without cheats. I cheated like a bastard when I was a kid). I don't remember if it was Final Fantasy VII or Spyro the Dragon.
Don't know much about the lego games (except that supposedly, they're good), but seeing as they're action games, it shows that your kid got skills.
My first finish was Golden Axe and Contra when I was the same age. I cannot even get near the last mission in Contra now so god knows how I did it then.
Lego games are a bit odd, the Starwars games were great and different for the time but the rest that followed were a bit boring for me. But Lord of the Rings is a nice exception, they made it open world with more things to do and the cutscenes with the movie dialogue is hilarious. If you're a fan of the Rings series you'll probably have a good laugh with it.