We feel the same. We are not feeling immediately getting older, but we realize aging in larger steps. When we are in our thirties we are realizing that we are no more teenagers, in our fifties we are feeling that the twenties are over. However, overall we always believe we are the same. We are not realizing that life is change.
Everything changes. Our body does not only grow older, he regenerates himself regularly. Cells are replaced, renewed, repaired. So from which point onwards are we different to what we were before? Is it one cell exchange or twenty or a million? When is a change a change? It is a matter of definition and to define something it is a matter of our mental state.
Our mental state is how we realize our life and experience the world. We can change our mental state, we can accept the change and realize that the moment is now and we are now, so we are in the moment. We are not yesterday or tomorrow, we are right now. And this now is changing constantly.