What does it mean to be young at heart?  I believe each individual's definition of being young at heart is different.  It comes down to our own thoughts about our personal well-being.  Optimal well-being can only be defined by ourselves.  Optimal well-being not only involves our thoughts on our physical health, but it also includes our mental and emotional well-being, social well-being, spiritual well-being, intellectual well-being, functional well-being, etc.
I think that my 77 year old grandmother is an excellent example of how someone is young at heart.  She always seems to have a good time.  She likes to have fun, has a good sense of humor and is always on the go...going out to lunch with her girlfriends, playing in her card club, participating in church functions and community organizations, watching sports (an avid basketball and baseball fan), and playing Wii bowling.  Through a family night event at her church, she has discovered the fun and exercise of Nintendo Wii bowling.  She has taken it upon herself to learn a new technology, how to play Wii bowling.  She teaches her senior peers how to play, engages them in friendly competitive games, and crowned herself the winner of "the old ladies division."  This game has created so much fun for her and is another example of how she keeps herself young at heart.  Not only should we look to seniors on how to stay young at heart, but we should share our discoveries with others.