You are as young as your faith, as old as your doubt; as young as your self-confidence, as old as your fear; as young as your hope, as old as your despair. ~Douglas MacArthur
To be seventy years young is sometimes far more cheerful and hopeful than to be forty years old. ~Oliver Wendell Holmes (Thanks Janice!)
Anyone who stops learning is old, whether at twenty or eighty. ~Henry Ford
When I was 40, my doctor advised me that a man in his 40s shouldn’t play tennis. I heeded his advice carefully and could hardly wait until I reached 50 to start again. ~Hugo L. Black
The idea is to die young as late as possible. ~Ashley Montagu