Negative caricatures of aging are far too prevalent in our culture -- and they are harmful. Simply telling people to think positively about aging doesn't work, because the mind is very good at thwarting such explicit lessons. There may, however, be a more subtle way to mitigate the deleterious effects of such caricatures.
You don't have to run. Play tennis, cross-country ski, meet a friend for racquetball during your lunch hour. Find a way to work your body hard on a consistent basis and don't decide if you're an optimist or a pessimist until that's the routine. You may not believe how much your outlook on life changes.
When routine, whether in action or attitude, becomes too comfortable or constrictive, it's often a clue we're limiting ourselves. There's an invitation waiting -- to look again and discover a new spaciousness. It's here, in this spaciousness, that we're better able to notice the big things and the little things.