A Strict Age Limit
To be a part of the FBI's street team, you need to be between the ages of 23 and 36. It might seem like this is an ageist requirement, but this is to make sure that the on-the-ground FBI agents are in tip-top shape. Once they go past the age limit, they can head into the office if they choose.
Surpassing the age limit isn't the end-all-be-all for FBI agents. They're offered other positions in the bureau, especially if they're a favored agent. There is a lot of space to move up on up in the industry.