Depending on the type of bleeding disorder and your family history, you may know you have one from birth, or you may be diagnosed as a young child.
Some bleeding disorders can have mild symptoms or no symptoms at all. So you may not find out until you are an adult, perhaps after having abnormally heavy bleeding when you have a tooth out or after having an operation. It is usual to do blood tests before surgery these days, so it may be picked up during routine pre-surgical screening.
You will need to have blood tests to get a firm diagnosis of a bleeding disorder. These are not generally routine tests and may have to be carried out in a specialist centre. You may also have to have a genetic test to look for the exact mutation in your genes that is causing the condition.