What does it mean to age healthily?

When looking into this course I imagined this whole aging idea referred mostly to the aspect of aging in terms of psychology, or the mental capacities and behavioral characteristics of aging. After our first day of class my ideas have changed a bit to look more at healthy living, in terms of physical characteristics like building a healthy body. However, I would like to define healthy aging as moving forward in life in a manner which keeps you close to the average bounds of your age range.  Whether this definition refers to psychology or physical traits this can be what defines healthy aging, one whose characteristics fit societal standards for their age group.  Though I would rather keep society out of this who idea.  With this definition I would say something like a 12 year old who is independent, responsible for herself, employed in a full time job, etc. would not be healthily aged.  I am still rather confused and curious as to what may truly be meant by this "healthy aging" thing so next I will do some research and come up with out others define it.