Grandad has just promised something he is unlikely to be able to fulfil. He then thinks to himself:
「いざとなったときもし逃げたりしたらわしゃこの年にして裏切り者のウソつき者じゃ。どうなるかわからんことまで言うもんじゃないのう。」
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.