I don't know how cold you get, I always prune to two or three buds above the one I want incase frost causes die back, then take the rest off in the Spring after frosts finish and before growth starts.
That old it may not be grafted, but growing on its own root. If you can't see an obvious graft at the base try making cuttings from your prunings, about 9-to-12-inch pencil thick lengths. Drive a spade into the ground at 45 degrees, and lift it a little. making a slot to push the cuttings in, and then heeling them in. Taking them just below a bud and using rooting powder helps.