President Joe Biden attends a campaign event in Wallingford, Pennsylvania, on March 8. Evelyn Hockstein/ReutersPresident Biden is hitting television airwaves this week with a minute-long advertisement that immediately addresses one of his biggest political vulnerabilities: his age.“Look, I’m not a young guy,” a smiling Biden, wearing a quarter-zip sweater over a white shirt, says straight to camera at the start of the 60-second spot. “That’s no secret. But here’s the deal: I understand how to get things done for the American people.” He goes on to list accomplishments like…