3. Keenan Allen
Outside of cornerbacks, receivers are probably the most prone to fall off the age cliff without warning. Once a receiver hits the age where his athleticism and explosiveness are not the same the numbers instantly drop and they are quickly out of the league.
What makes it more concerning is when a receiver over 30 suffers a lower-body injury that hampered most of last season. That is exactly what happened to Keenan Allen as a lingering hamstring injury caused him to miss more time than it likely would have if he was 25.
That being said, there is more reason to be optimistic about Allen's chances to stay relevant in the NFL hierarchy. While some Chargers fans have weirdly already given up on Allen, the veteran receiver still played really well once he returned from injury last season.
Plus, Allen's game is not predicated as much on athleticism and explosiveness as it is route-running. He showed in 2022 that he can still run some of the best routes in the sport and that will at least add some value to him regardless how he ages.
However, there were also games (against the Raiders) where he couldn't buy man separation to save his life against mediocre cornerbacks. If there is any game tape that would make fans worried about Allen's aging it is the tape against Vegas.
Just to get an idea of how quickly this can happen for an NFL receiver, go look at Julio Jones. He was a Pro Bowler at 30 years old, got hurt and played nine games at 31 (but was still good) and then fell off a cliff production-wise at 32. Jones' age 31 season and Allen's age 30 season are very very similar, so keep that in mind.