Lots of good points to consider, Barry - yes, of course age is a factor, and the age at which the different insurers jack up the premium or refuse to insure you at all is another thing that varies hugely.
Insuring as separate individuals rather than as a couple might seem advantageous, but in fact you'd need to declare the PCa on both policies, because if the holiday had to be cancelled because of it, you'd only both be covered if you had both declared it.
Obtaining insurance that excludes cover for the PCa is an option, but simply not declaring the PCa is not the same. Some companies simply don't cover you for conditions you have chosen not to mention, but most of them say they want you to declare everything, and it may invalidate the policy if you don't.
The variation in cost and conditions of travel insurance are much bigger than those in motor insurance, so it really is worth shopping around. Another contrast is that if you make a claim with one company, you can reinsure with another company without having to declare it - unlike car insurance where your claims record follows you for about five years.
We were just grateful to have found the Nationwide cover, as no one else seemed prepared to insure us at all at that stage without charging more than the price of the holiday.