I would say for now call your insurance company and ask if they offer something like this.
I've found some helpful info here too:
Have a nice day.
it depends on the country/state you're in...however, usually, car rental companies are MORE than happy to sell you the required insurance - although it is a lot more expensive than if you can get the coverage through your own insurance company...
so, if you can't get the coverage through your insurance company (you CAN always get it "temporarily" if it's just the *cost* that's preventing you - all you do is ask your insurance company to add on the coverage, and then call them up and request them to remove it once you're home from your trip), the car rental company should be able to help you out - as well as themselves ($$$), lol.
good luck.
In the USA most companies require you to be 25. There are a couple who will waive that age requirement. I believe enterprise is one. As for the insurance, you can simply buy the rental cars insurance offering
you can purchase the insurance from the rental company it's cheaper
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