As long as the brake fluid is the correct spec I wouldn't worry. Unless you drive a very heavy car down a very steep hill , very fast regulary, you aren't going to have much problem.
Don't use fluid that has sat in an open bottle for any period of time though. It is hygroscopic.
I've had my car for a year now, I know it's had oil and filter changes but not sure if it has had a break fluid change. When I had a service they said the fluid was ok, should I still change it? I'm guessing they won't be able to see how much mositure there is In the fluid.