I'm 35 years old and still on my parents car insurance policy because it's cheaper as there's a discount since multiple vehicles are insured through the same company.
I've never heard about a certain age that you had to be off your parents car insurance policy and they've always kept me insured on my parents insurance because it's cheaper.
I just pay my parents the money and we both save because there insurance rates are cheaper as well as mine.
Now there is a limit to staying on your parents health insurance which is 26 years old and after you turn 26 years old you must get your own health insurance and can no longer be on your parents health insurance but car insurance is different.
You can stay on your parents car insurance as long as you want at least that's been my experience and they've never said anything.