Discover and AmEx market heavily to university students, or at least they used to. I had both within about two months of starting college, when my checking account was only two months old itself, and actually managed to survive without a Visa or MC for almost a decade till I broke down for the UA 20,000 mile bonus. Back in the day, AmEx had a partnership with Continental which included two vouchers for $249 round trip tickets anywhere in the lower 48, quite valuable when you're in a small town on the opposite coast as your family.

For the last 10-15 years, the threshhold for revolving credit has dropped precipitously. CC companies, like all companies, want to gain name recognition and loyalty among younger customers, and it's progressed from college graduates to college students and now you see news reports every now and then about some high school student who's run up an unmanageable debt load.