Hi Deb,
Congratulations on providing your lovebird a home that has allowed him to live so long! At this time, however, you must take him immediately to an avian vet in order to let him recover from this problem.
He likely has a respiratory infection which is backing up into his mouth or he may have a crop problem. It simply can't be diagnosed online, even by a vet (which I am not). If you do not have an avian vet, go to http://www.aav.org/ and locate on near you, calling immediately to tell them of the urgency so they can work you in immediately.
In the meantime, keep him as near 85 degrees as possible. Do this by placing a heating pad over (or under if he is sitting low) 1/2 of his cage. Then cover three sides of the cage to keep heat in. If you see him open his beak in act as if he is "panting" then he is too hot. But be sure to leave space so he can move toward or away from the heat to be comfy.
There is no home cure for this problem, nor can you get a pet shop product that will fix it. Because of his age and the fact that the problem sounds quite severe, rushing him to a vet is very very crucial to ensure his survival. So, please call right now! I'm sending some links for reading, but please do not take time to read them before calling the vet!! Immediate emergency help is crucial.
I'll be pulling for you and your little lovebird!
Signs of illness: http://www.birdsnways.com/wisdom/ww14ev.htm
Care: http://www.avianweb.com/sickbirdcare.html
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Breeder
over 25 years breeding, taming, training parrots.