Sammus,
Enter "boolprop testingcheatsenabled true" in the cheat prompt, shift-click your sim, click Spawn>tombstone of l&d, click the tombstone, choose "add neighbor to family", and look through the list by clicking "more" if you don't see their name. When you see their first name, click on it and then they will be a household member. Make sure you have the game paused while you look for your friend's name. Once they are a family member they will be able to age. To make a teen grow up: enter the boolprop cheat, select the teen, shift-click the teen, click "set to birthday", click the teen and choose "grow up". There you go!