[JustinOpinion]

The only valid reasons I can think of for a dealership to decline a test drive would be: 1) You too young and cannot be legally liable for any damages; 2) You have said or done something while visiting to give them legitimate reason to consider you a risk or a person who is not a serious buyer; 3) The car you want to drive is already SOLD or on hold for a buyer.
In the case of #1, bringing an older adult along should resolve that. I would thank them for their time and let them know I'll be shopping and buying elsewhere, then leave. If you feel like you need more satisfaction, make a call to the district manager for Chevy or write Chevy a letter (the real kind, that you mail). They will bring one to your house for you to drive!