A 20 year old bud was able to rent in Ann Arbor, MI a few years ago--- no corporate acct. or anything. He had to pay an extra underage fee (I think it was +$10/day for 21-24 and +$20/day for 18-20.) He needed Thrifty segs for a promotion, and in my research, I found that age policies varied widely by location. I remember Lexington, KY allowed drivers 18-24 for only $5/day.
Call the location, or sift through details of rules on travelocity, and you'll eventually find specifics for your location.
Which city are you looking at?
[This message has been edited by Viajero Joven (edited 12-06-2002).]