It's true, though, skill is limited in the NFL outside of QB..QBs can still play at a high level late into their 30s because they have a unique talent and set of skills that allow them to be effective..every other position player in the NFL dies at age 30, even the biggest name players, because it's all physical and relatively limited skill..there are exceptions, of course, but those dudes are anomalies..
In every other pro sport, you'll still see an abundance of older athletes that are past their physical peaks, yet still playing at a high level due to their skills..NBA, soccer, MLB, NHL, they all require immense skills..