nah that can't be. I've had so many test drives in cars it's not even funny. I don't think I was 18 when I was test driving cars.
if you DRIVE IN to the dealer in a car, you should be able to TEST DRIVE the new car. I drove a bunch of jeeps for heck of it when I was 17-18 ish. I was alone, and they didn't say anything. I just handed my license to them and went for a drive. Sometimes they went with me, sometimes they didn't.