Aaron Carter, the younger brother of Backstreet Boy Nick Carter, proposed to his girlfriend Kari Ann Peniche on stage last night in Las Vegas, a source tells Us. Carter initially planned to go directly to a local chapel but decided a proper wedding needed some planning. The couple reportedly plans to wed in the next six months. Peniche, 22, was named Miss United States Teen in 2003 but had her title revoked after she posed for Playboy. According to her MySpace profile, updated yesterday, she is currently single and does not want kids. She might want to update that. Carter, 18, is the youngest solo male singer to have four Top 40 singles. "House of Carters," a reality show about his life with brother Nick and their three sisters, premieres next month on E!. The engaged pair stayed at the Palms Casino Resort. It will be the first marriage for both. Carter's rep could not be reached for comment.