Aging is sometimes called the great humbler. Some embrace it. Some dread it.   But most of us vacillate between the loving the good parts and resisting the reality that our bodies and brains have a limited shelf life. What does that mean for our quality of life? Aging is an involuntary invitation to seeing how we are attached to who we want to be and where we are afraid to let go. But if we shift our attention in a certain way we might find our ideas about aging aren't quite as concrete as we thought.