Ben Affleck hasn’t lost anything on his fastball. That’s according to his wife, actress Jennifer Garner, who seemed to get a little indignant when David Letterman poked fun at Ben on the occasion of his 40th birthday Wednesday. Told by Garner that Affleck isn’t happy about getting older, Letterman said, “What’s the problem with him? Is it low T?” Garner looked stunned. “Are you asking about Ben Affleck’s testosterone level? Really, David?” she said, laughing. “He will stomp you. Have you seen my husband lately? He is walking testosterone!” Wethinks she doth protest too much. That said, Ben does look pretty buff on the set of his new movie, “Runner, Runner,” which costars Gemma Arterton and Justin Timberlake.