A pensioner couple, both about 80, were on a sentimental
holiday to the town where they first met. They were sitting in a pub and
the
man said to his wife, "Remember the first time we had sex together, over
fifty years ago? We went round the corner to the gas works.  You leaned
against the fence and I gave you one from behind."
"Yes", she says, "I remember it well."
"OK", he says, "How about taking a stroll round there and I'll give
you one for old times sake?."
"Ooh George, you devil. That sounds like a good idea," she answered.
There was chap sitting at the next table listening to all this
and having a chuckle to himself. He thought, "I've got to see this, two
geriatric pensioners having sex against the gas works fence." So he
followed them.
The couple walked haltingly along, leaning on each other for
support,aided by walking sticks. Finally they got to the back of the
gas works and make their way to the fence. The old lady lifted her
skirt,
took her knickers down and the old man dropped his trousers.  She
turned around and hung on to the fence just as the old man moved in.
Suddenly
they erupted into the most furious sex the watching man has ever seen.
They were bucking and jumping like eighteen-year-olds. This went on for
about forty minutes.
The woman was yelling, "Ohhh God!"  and the man was hanging on to
her hips for dear life. This was the most athletic sex imaginable.
Finally,they both collapsed panting on the ground. The watching guy was
amazed.
He thought he had learned something about life that he didn't know.
He started to think about his own aged parents and wondered whether
they still had sex like this.
After about half an hour of lying on the ground recovering,
the old couple struggled to their feet and rearranged their clothes. 
The guy, still watching, thought, "That was truly amazing.  He was going
like a train.I've just got to ask him what his secret is."
As the couple tottered past, the chap said to them, "That was
something else. You must have been shagging for about forty minutes.
How do you manage it? Is there some sort of secret?"
"No, there's no secret," the old man gasped.  "Fifty years
ago that fucking fence wasn't electrified."