What do you mean by growing old?

To me, growing old is losing the subtle sensibilities that stimulate your feelings and thoughts when you encounter the slightest changes in your usual daily life.

I have so much to say, to reflect on before, everything around me can give me some idea and thoughts and all these feedbacks from the environment make feeling alive. The older I grow though, the less I had the kind of feeling. I almost have nothing to write now. Is this the real truth of growing old?

And where is the zest of life?