I can’t even make my signature look the same from one day to the next (dang my sucky handwriting!); you’re right: a 70-something-year-old man producing the same signature that he had in his early 30s is more than a little difficult to believe.
These antics are almost laughable.
In my research this year, I found a 1768 signature in a will that matches with a 1817 signature in a deed. It's the little loops and tick marks that are still there.