If the OP is going to use career achievements to discredit GSP, then their ages are completely relevant. For all we know, by 36, GSP might be finishing every opponent he comes across in devastating fashion, just like Silva.
Assuming both fighters began fighting at a similarly young age, I would say what GSP has achieved at 29 is damn impressive.
So now you are trying use the future to back up your argument? For all we know when GSP is 36 he could have been KO'd 5 times in row and hadnt won a fight in years, its all completly irrelavant. We are talking about current records here not about what ifs and Of course what GSP has acheived in his career is damn impressive no one can dispute that, but the fact is at this present time Andersons is way better.