What kind of knee surgery did you have?
When a professional athlete has knee surgery and returns to the field (I think it usually takes about three or four weeks, even in the fastest cases), it’s generally arthroscopic and minor. They might cut away some cartilege or clean up a little scar tissue from a previous surgery. They have a few pretty big advantages in their recovery.
First, as you mentioned, they’re 24. Young bodies heal better than older bodies do.
Second, they’re probably in better shape to begin with. A big part of the recovery from minor knee surgery is working the muscles around it back up to full strength. If the muscles are exceptionally strong to start with, it’s easier to get them working faster, and it’s easier to function relatively normally before the muscles are back to full strength. If they’re not that strong to start with, there’s a longer road to recovery.
Third, they’re rehabbing in the highest quality facilities, overseen by personal trainers and/or team training staff. For a professional athlete, rehabbing his knee is his job. He getsup in the morning and begins rehab. He doesn’t have to squeeze it in before or after work, or rush through it because he needs to go pick up the kids at 6:30. That’s the sole focus of his workday. And his rehab is a whole lot more aggressive than mild isometric and other exercises.
Finally, I’d bet the professional athletes who have knee surgery and return to the field in three weeks aren’t playing at full strength, and they aren’t playing without pain. They might have a shot of some kind of painkiller in the knee before the game and another at halftime if it’s bad. But professional athletes are used to playing through pain. As long as they’re not likely to reinjure themselves, they’ll tough it out. In some cases, they’ll tough it out farther than they should and do reinjure themselves.