Grandad has just promised something he is unlikely to be able to fulfil. He then thinks to himself:
If push came to shove and I were to do something like run away, I would be a liar and a traitor. I shouldn't go as far as to say that I don't know what will happen.
I translated この年にして as 'at this age', but I don't see the relevance. If he fails to fulfil his promise he'll be a liar and traitor whatever his age. What have I misunderstood?
The second sentence also seems unconnected. I must be missing something here.