If your posture is not very good, and the curvature in the spine and neck are too deep, then yes, by stretching up and reducing over-curvature, you can gain quite a few centimetres. I have had clients who, after using a gravity inversion table (hanging upside down) have grown taller, simply by straightening out. Remember, you don't actually shrink with age, you are merely sinking deeper into the curves of your spine and neck. This can be prevented by working on posture and with gentle traction (a form of stretching) using a gravity inversion table. Read my hub "Hanging Upside Down" for more detailed info.