Personally I wouldnt do it being that old of a dog. Tails are there for more than wagging, the dogs balance will be thrown off for awhile, its will have a learning curve when it come to walking/running again and even more when it comes to swimming.
This is just my opinoin based on my one and only experience, 5 days after his tail was cut off he was back to jumpin the 5 foot chain link fence and roamin the neighborhood.. He was a stubborn hard headed son of a gun though.. so maybe he was the oddball..
