All is good!
I went back to the Columbus Direct website and realised that I had entered 70 as my age - but it is current age, not that at time of travel, that is required. Bingo! All covered for my 82-day trip next year.
Insure and Go also worked (they made a very definite point of saying to enter current age, not that at time of travel.) A little hard to make an exact comparison, but they seemed a tad more costly than Columbus. They also listed the countries they won't cover - which was handy, rather than filling out a list and then copping a rejection.
The upshot is from this little exercise that once turned 70, it looks like various significant changes occur. The duration of a trip limitation looks a real PITA.
Anyway, I'm now able to ignore it until next year!