US President George W. Bush, who turns 60 on July 6, joked that six decades is "not that old" and blamed his gray hair on his twin daughters' teenage antics. "For you youngsters, I want to tell you something: When I was your age, I thought 60 was really old," he said during a speech on immigration. "It's all in your mind. It's not that old, it really isn't." Earlier, during a roundtable with immigrants to the United States, Bush joked with one father of two young children: "You think my hair is gray because I'm president? No, my hair...