How old do you have to be to test-drive a car?

Answer:

First you must be a serious buyer. They don't waste their time with joy rides. Second you need to be 18 or over, the age at which you can legally enter into a contract, or have someone 18 or over accompany you who would be a co-signer of the contract if you did purchase a car.

That is how the sales person earns a living, and they don't appreciate people who waste their time and keep them from a customer that will buy a car.

Can you get new auto insurance if you let your old policy expire?

New auto insurance
There might be an internal "30-day rule" within certain companies, but you can get insurance with a new company. You may have to do a bit of footwork, and it might not be with a standard carrier, but it is possible.

A carrier with this "rule" is probably just wanting to verify what kind of customer you'd be, particularly in the area of premium payments (are you always on time? regularly late?). Insurance companies are, after all, businesses ... they want to know you'll be a good client.

Do some shopping around, though, and you'll find coverage. Once you've established coverage, however, remember to go back and do some more shopping, especially for better rates.