Why is everyone saying T-Mac is washed up and should retire?

Tracy McGrady is only 31 years old (respectfully) which is the same age as Kobe. I'm not saying T-Macs better than Kobe cause he's not, but before his injury people were debating who's better McGrady or Kobe. He only played 24 games last year so how would you know how much he's still got left? Guards can play up to until 36-38 years old proof would be Grant Hill(37) and Steve Nash(36) (respectfully)