Joey (2004)

After his friends all go their separate ways, Joey Tribianni leaves New York for Hollywood to pursue his acting career full time. His slutty sister Gina buys him a nice apartment, and he finds a new roommate in his 20-year old nephew Michael (Gina had him when she was 16), who is literally a rocket scientist. Michael's book smarts and Joey's people smarts allow them to help each other out whenever they can, and make them nice companions.