Kid Rock is going to be a grandpa at the ripe old age of 43. The rocker's 21-year-old son, Bobby Ritchie Jr., is expecting a baby girl with his girlfriend, sources tell Us, adding that the couple is four months along. Ritchie is Kid Rock's son with the rocker's ex-girlfriend Kelley South Russell; Rock raised the boy mostly on his own. For more extremely young celebrity grandparents, click here and here. (More Kid Rock stories.)