 And in an era when other people his age put troves of personal information online, Thomas Matthew Crooks, 20, left few clues about who he was, what he believed, or why he decided to drive to a Trump rally in western Pennsylvania on Saturday and try to assassinate the former president. How old was John Wilkes Booth, Lee? I think he was 26. Get it up on the screen. And how old was Lee Harvey Oswald? I think he was 23.