Complex sentence: Elderly people are very prone to this disorder because of the decreased mass of their gray tissue, for instance the stereotype of the wise-cracking grandfather may have originated from as it became a common part of every day life.
Split into simpler sentences: Elderly people are very prone to this disorder because of the decreased mass of their gray tissue. For instance, the stereotype of the wise-cracking grandfather may have originated from this as it became a common part of every day life.