Jay is right, the vet can check him up real quick and found the reason why he's not eating. It could be some type of diabetes too...so you did good to go to the vet and not to wait.
I'm glad to hear that you'll be taking your dog to the vet. There are many things that could be going wrong at his age, and some pretty routine blood and urine tests should get you an answer. Since it sounds like he's got an upset tummy, you can try giving him a Pepcid or a Zantac tablet in the morning, and maybe even a Tums for good measure later in the day. Since he's lost his appetite, you'll probably have to pill him - just stuff it down his throat until it's past the point where his tongue rises against the roof of his mouth. If you're really quick, it shouldn't bother him a bit.
You might call your vet today if they're open, and see if they'll do a payment plan or if they accept Care Credit. You can also go to the Care Credit web site and apply yourself. CC is a line of credit to be used only for medical bills for humans or animals. Make sure you read the fine print, as I recall that any missed payments result in an outrageous interest increase. It's nice to know it's there in case of emergency though. :-)