it is my sons birthday so i will not be around until later this evening.here is what i suggest for the first step
move the fish to a quarantine tank (preferrably a 10 gallon)or a large sterilite container or other food safe container.a clean and sterile 5 gallon pail will also work in a pinch,if you have one for water changes.
use epsom salt,pure 100%magnesium sulfate is what you want,dose at 1/4 teaspoon per 10 gallons of water.this can be found at any pharmacy.
add an airstone for extra oxygen.
we will see if there is any improvement after 24 hours.
if the fish is already pineconeing,this is dropsy,a symptom of a bacterial infection.try to get your hands on one of the following: metronidazole,maracyn 2,tri-sulfa or erythromycin and if all else fails tetracycline.these are broad spectrum antibiotics.use as directed.add an airstone when performing any treatment.you should also use this in quarantine it will kill off your bacterial colonies.
as jaysee mentioned,this is the normal"old age" for goldfish. they can live longer,but this is typical.
i also suggest that you get a liquid test kit.perform large (75%)weekly water changes in your main tank and clean your filter media atleast every 2 weeks in dechlorinated water or old tank water.
i will check back this evening,good luck.