DH and I have always had Gieco. We paid about $1k every 6 months for both of us with great coverage and driving records. Adding my 16 year old caused it to double. I got a quote from every co I could think of and they were all higher than Gieco.
I also learned that waiting until she turned 18 to add her would not have made a difference. I was told that it's not really based on age, but based on driving history. If I added her at 16, 20 or 30 it would have been the same because she would have zero driving history.
Also, for CA you can't assign the teen the car. She gets assigned to the most expensive car on the policy, whether she drives it or not. Which is really annoying. DH and I drive new cars, she drives an older Honda Civic, yet she is tied to my husbands new truck that she NEVER drives and couldn't possibly wreck.
We tried giving her her own policy with her civic, that didn't work either.