re: NFL QB’s that played way past their prime and were washed up

I think the reason Manning's drop off was so sudden and severe was that he had a degenerative nerve/spine issue which impacted his grip strength. He was never the same from a physical standpoint after coming back from the surgeries, his passes were noticeably weaker. It's really amazing that he was able to have that record setting season with Chad Pennington level arm strength. He hit the wall and his body was breaking down in that final season and a half or so