Can't say for sure on the snakes age. I've only had him for a week and was unable to track down the original owner. Not that it helps any, but I know that it has gone through at least three owners prior to myself. I'm going to guess between 2 and three years old due to its size (9' plus) and the fact that the individual I got it from tells me that it was severely underfed when he received it six months ago. He says that he brought it a long way, but it still appears to be a little underweight to me. It is setting right now about 22lbs and I'm assuming that it should be up around 30 at this length? I had it to the vet to get some anti's for its respiratory infection and did mention the frequent urination. Didn't get much of a reply from him though so I figured I'd poll the posters on the site for a general consensus.
How old is your snake? There could be many reasons for frequent urination. It is possible it's just your snake's preference, but assuming not...
Kidney disease results in the inability to concentrate urine. You may also notice increased drinking. Blood tests can usually rule this out.
Masses (abscesses, injuries, tumors) can physically press against the bladder (brain fart here, do snakes have a bladder or is the urine stored in the rectum with the feces; can't remember), or the rectum thus not allowing the storage of larger amounts and forcing more frequent urination.
Hormonal and physical problems can lead to incontinence but are not well documented in reptiles.
A vet visit is not out of the question and a thorough exam along with a blood screening will allow for the detection of problems in an otherwise healthy looking snake. Early detection=early treatment and better prognosis.