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There are a variety of possibilities for a 7 yr old dog suddenly starting to have accidents in the house. The first thing I would think of was a urinary tract infection. When this occurs, there is an increased urgency/feeling that Khan has to pee and he just can't hold it until you let him outside. There may be no other signs (liked increased drinking), although sometimes there might be some blood in the urine. You will need to take Khan and a fresh urine sample to your vet for analysis as antibiotics are required to clear up an infection.
Bladder stones are another possibility. Often a bladder infection will go along with the stones. You didn't say what breed/size of dog Khan is, but there are some small breed dogs (like Bichons) that are prone to stones. If your vet thinks there could be stones, he/she will want to take an x-ray. Some stones (struvite) can be dissolved with diet, but other stones (calcium oxalate) require surgery to remove.
Endocrine diseases, such as diabetes or Cushing's disease (an over-production of steroids) can cause increased urination. You will also notice Khan drinking more and possibly eating more. With diabetes, there will also be weight loss. Both of these diseases are treatable, but need to be diagnosed by your vet with blood and urine testing.
Kidney problems can cause a dog to drink more and then urinate more. Again, blood and urine testing will diagnose this problem.
Some older dogs can become incontinent and leak some urine when they are asleep and relaxed. This is more common in spayed females than in males, but it can occur.
Prostate enlargement, infection, or cancer can make it more difficult for a dog to urinate and he may not be fully emptying his bladder outside, so he ends up urinating when he comes in. A rectal exam will help make this diagnosis.
Behavior issues can also be the culprit, but I would consider it less likely in a 7 yr old dog with no other problems.