Car insurance providers discriminate against young drivers for similar reasons: you're more risky. I wouldn't entrust the care of my entire house to college students.
The US has a very long history of racism against minorities. It's been difficult to get a strong system in place to combat racism. Ageism against young people has a built in correction system called aging.
I wouldn't even rule it out entirely, you'd just need references (a decent rating).
The same age group is faced with similar problems renting apartments because they often lack credit ratings and previous references.