My coworker rented a Navigator from MSP and I returned it. I was 24 at the time, but they just asked if I wanted it on the same CC, and I said yes. I got the receipt and walked off. For all the check in guy knew, I was my buddy (who has a good 10 years on me, if not more).
I wouldn't worry about it, but if you get in an accident or something, things could get hairy, especially if you're relying on any insurance from hertz.