Unfortunately most people do not understand about bipolar disorder unless they have found it necessary to learn by having a diagnosis thrust upon them. There is so much misinformation out there. I would suggest that you learn as much as you can about the disorder and about the various treatments that are currently available, and then pass on the information to your parents.
In your reading you will learn that the longer a person with bipolar disorder goes untreated, the worse the symptoms become. The episodes usually start to get closer together and there is less and less "stable" time between episodes. The illness does not go away as one gets older. Because this is a biochemical disorder of the brain, when it is left untreated, there is a physical deterioration of the brain that you can see in a CT scan. Symptoms that might have been controlled fairly easily near the beginning become much more difficult to treat as time goes on. These are just a few of the reasons why you might want to reconsider refusing to take medications.