I actually don't think most people think this. I think most people HOPE that top players extend their time at the top, but are well aware of the evidence that it's unlikely.
Soccernomics has their research saying most players peak at 27 IIRC. And that seems to be commonly accepted. Hence why there are so many revelatory articles about players 30+ continuing to do well, Mo for example.
If listening to pundits has taught me two things it's this:
No former players know the actual rules and what is or isn't illegal should be decided by how they feel about it.
No former players can overcome their previous team allegiances.
This is an awful idea.