My Insurer now is Easy Travel, and they don't seem to have an age limit on their policy (underwritten by CoverMore)- they just say that higher risk age groups may attract a higher premium.
They insure me for skiing with 2 total knee replacements and osteopenia, high blood pressure (controlled), high cholesterol, and leukaemia, all for a very reasonable Existing Medical conditions extra fee (in the hundreds of dollars, not thousands). I have never needed to make a claim, so I can't say how they are that way, but it's another option to add to the research by
@bpc above.
Bizarrely, CoverMore themselves directly will not insure my leukaemia, but it is expressly covered as a stated condition for Easy Travel (who issue a CoverMore policy)

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It would definitely be worth their while to check around. Also be aware that some car rental companies impose age limits on rentals for older drivers too.