I have an open brain, and have only seen its tentacles out a couple times. I figure if it's not hungry, it's not going to bother putting the tentacles out. I've had my brain for a long time too, and it's healthy. So I'd say not to worry unless it's physical appearance starts looking unhealthy.
Related, I've never ever ever seen the tentacles of my candy canes or trumpets. And I've had the trumpets for almost 2 years.