Don't squeeze him! Don't feed him at all for two days. When this time has passed, buy a bag of frozen peas, thaw them and pop them out of their shells and feed him with these. Always keep them in the freezer and only thaw the amount of peas you want to feed to your fish. This way they will stay fresh for longer (: I heard that worms or some epsom salts also work as laxative for fish!
If he won't get any better after a couple of days with this new diet, he might have a problem with his swim bladder, and then you would need to treat him with salt, make a 50% water change, remove any live plants, and add 1 tablespoon per 5 gallons of water. Keep the water well filtrated and aerated during this time of treatment.

A varied diet is important for goldfish of any age, so if you've been feeding him with staple pellets or flakes all his life up until now, it's quite understandable that he got some digestive problems So no matter what, you should start giving him some live/freeze dried foods and vegetables like cucumber, peas, lettuce... C: It will make him stay healthy and happy many years longer! (:

 thanks for all the info, will try 2 days fast than epsom if needed. Brine schrimp,cuc,water fleas, epsom,spinach, lettuce and peas pureed, frozened in small cubes than thawed before feeding or  recipe close to it.