Alright, so it has been beaten to death that balance boards (hence their name) assist in improving your balance. However, it was also briefly stated that they have other advantages for fitness. You would not think it at first, but balancing on a board will engage your entire body. This includes your core muscle groups and, obviously, your legs.
But, besides balancing, there is one major area where these devices assist in fitness. It was addressed previously but it goes far and beyond just the elderly. Balance boards are terrific for those who are dealing with a nagging injury and are rehabbing. Clearly, you will need to get consent from your doctor (as they will know more than we could ever tell you) if you could use one. But, they will significantly help your joints.