One thing I notice about people getting older, is that many of them have forgotten or don't take the time to play. Playing can be anything from physical exertion to mental stimulation. We stay young if we continue to move our body parts and exercise our brains. Read this post, Finding My Play, by Ann Mehl.
"We are designed to find fulfillment and creative growth through play, but we so often say that we don’t have any time for it. We have been taught that the most successful person is the one with the most money, prestige, strength, speed or power. But yet, the happiest person is often the one having the best time."
What wise words! Now go and be happy, have some fun. Call your friends and ask them if they want to come out and play. Schedule a play date. Be creative, get excited. Learn, stretch, grow, laugh!