In the US, at least federally, you are protected against age discrimination only if you are over 40. You can discriminate against younger people on the grounds of their age all you want.
Which, incidentally, governments on all levels (federal, state, local) happily do all the time with inconsistent ages of majority depending on the topic at hand:
16: Age to get a driver’s license.
18: Age to vote, enter into contracts, buy a rifle or shotgun, legally considered “adulthood,” except…
21: Age to drink, smoke, or buy a handgun, and…
25: Age before which no rental car agency will rent a car to you. (Go figure.)
In the US, at least federally, you are protected against age discrimination only if you are over 40. You can discriminate against younger people on the grounds of their age all you want.
Which, incidentally, governments on all levels (federal, state, local) happily do all the time with inconsistent ages of majority depending on the topic at hand:
Don’t forget hotel rooms!