Juggling boosts grey matter in the brain.

Helping your brain is more than just performing mental tasks.  Our brain is hardwired in such a way that performing physical activities can actually help across a wide spectrum of cognitive tasks.  One positive aspect of incorporating these tasks is that they are often less tedious than mental tasks.  Some of them are plain fun.

Learning to juggle can be difficult at first, but once mastered, it's like riding a bicycle, you will always retain the skill.  Many people start with scarves or some kind of fabric.  The fabric moves through the air slower and is easier to grab while also being more forgiving of mistakes of hand-eye coordination.
Here's a great place to start learning how to juggle.

Don't worry if it takes you a while to get the hang of it, you're actually doing More for your brain by simply attempting the new task, than an accomplished juggler is by practicing.  The accomplished juggler can probably toss balls in his or her sleep, while the beginner is constantly forcing the brain to make changes in order to accomplish this strange new task it's been given.  In that spirit, try to learn something new every day, even if it's just a small, simple task.  The more the brain has to adjust, the more it gets used to adjusting.  It is my belief that this is important for the overall health of the brain.