Just curious: why do age discrimination laws only disallow discrimination against older ages? Even if discriminating against people age 20-30 is more rare, wha

Just curious: why do age discrimination laws only disallow discrimination against older ages? Even if discriminating against people age 20-30 is more rare, what's the advantage of allowing it? It seems like a hard sell to say "you should care about age discrimination" but to enact age discriminatino laws that literally discriminate based on age. Maybe this moral inconsistency is why more people don't care/do more about it.