"If you're not having fun, you are not learning." That was my teaching motto during first lecture of Data Base Theory and Administration at Golden Gate University. Fun and learning go together. Children at play learn effortlessly. School gets too serious and we forget that learning is a natural human pleasure. Life itself is the school. During class a student suddenly echoed back: "If you're not having fun, you are not learning!"
Learning is ecstasy - naturally moving us outside ourselves. We are born learners. Humans learned to live on land, the sea surface and underwater, and outer space. There is a pleasure in learning about anything. In extending ourselves personally and collectively into new frontiers.
If you want to stay young keep learning something new everyday. Open up a different kind of magazine. Keep changing the environment what you're looking at so that your mind works at mastering new vistas. You're old when you can't be bothered learn new things.