John Cena comments on when he made the decision to retire:
“As much as I love feel and I love passion, I also love data. I’m a strength athlete, so I consistently test one-rep max. I test vertical jump, all of these metrics — whatever they tested at the combine.
“When these numbers start to go down, you look at it like, ‘Okay, why? I’m getting plenty of rest. I’m training on a regular schedule. I’m not eating like garbage. I’m hydrated. My caffeine intake is monitored. All the data lines up. You should be strong.’ And then you look at the age graphic, and you’re like, ‘Oh, man.’
“The game just looks too fast for me, because it is. I could change my style at the risk of ruining that energy that WWE invested in me. And that’s tough, because from an ego standpoint, you’ve got to step away from the audience. I love it. It’s great, but that’s not respectful to the fans and it’s not respectful to the company.”
(Source: Sports Illustrated)