Some insurers would not take him on at that age. Also work out how much you have paid in premiums over the years and how much they have paid out - is it worth it or would you be better putting money away each month in case of vet bills. Maybe not with this dog but a lot of people never claim so if they had put the money in the bank they would be quids in.
All depends whether you could find the money if there was ever a big vets bill, if you could not, then insurance is a good thing. Compare the prices with some other companies but if you are happy with the one you are with why change? Maybe look at changing the cover, you might not need all they offer now he is older.