ANSWER:
Happiness is the quality which does not differentiate a young-old from an old-old.
Step-by-step explanation:
Happiness is the only factor which does not differentiate the old-old from young-old. This factor does not depend on any condition and age and comes from different sources and forms. Happiness can be gifted to anyone. The factors which usually differentiate an old-old with a young-old are health, money and etc.