John is 58 years old and is worried about declining mental ability in old age. he asks what he can do to prevent it. his doctor does not give him which piece of advice?

His doctor does not tell him to do nothing and not worry about it. Maintaining mental acuity is very important as the body begins to age, and his doctor knows this. It also must be actively maintained through a healthy lifestyle, which John's doctor would likely advise him to lead.