Protect the brain from injury. The skull is really hard but the brain is very soft. Some parts of your brain are more easily damaged than others, especially the parts involved with memory, learning, and mood stability. Wear your seatbelt when you're in a car, and wear a helmet when you ride a bicycle or motorcycle. Boxing is very bad for the brain because your head is banged repeatedly; hitting a football with your head many times may also cause problems.
People who keep their brains active can make their brain work better. There is no reason why your brain will get worse when you are old. The problem is that often we stop learning things and having new experiences. Your brain doesn't like this and switches off. So, when later in life you suddenly try to learn something new, it can be hard for your brain to start up again. Every time you learn something new, your brain makes a new connection. Learning sends more blood to your brain. People who keep their brain active still have a good brain when they are 70 or 80. Try to learn something new everyday of your life.