Something all life has in common is growth. Plastic does not grow. Metal does not grow. Let's not confuse swelling or shrinking with growth. Growth is the multiplication of cells making additional mass.
Like thousands of other technologies of which we have learned in nature that we cannot reverse engineer, growth is one of them.
We sense this spiritually in our lives. If we are not growing, things are not quite right. It is wrong to discipline ourselves to avoid things that do not earn money. We find ourselves attracted to learning because it is a type of growing. We like stories when someone changes because growth is life.
This does not stop at a certain age, unless you inflict dying on yourself by refusing to learn or grow. You may feel "old" because others see you as older but you have never been this age before. This is a new stage and you must either discover or invent growth for you life now.
Nature is our teacher. Your life is your canvas and you are the artist. Make your life beautiful.