Your grandmother sounds like a great lady indeed and I think you are blessed to have her, someone who is the way she is!
I agree; age is not necessarily a question of years but a question of heart and mind. If you are young at mind you ARE young.
"Now here's my secret", said the fox, "it is very simple. It is only with ones heart that one can see clearly. What is essential is invisible to the eye."
("The Little Prince" by Antoine de Saint-Exupery)
"The soul would have no rainbow, if the eye had no tears."
(Native American Proverb)