The full title of the book by Barbara Strauch is, "The Secret Life of the Grown-Up Brain: The Surprising Talents of the Middle-Aged Mind."
The book was full of information from the latest brain research, which is contrary to what most people have been told all their lives. Sure, you can kill off brain cells through various activities, but unlike what we were told in our youth, OUR BRAIN CAN GROW MORE. And guess what helps your brain grow more better cells? Healthy diet and exercise. Anyone surprised?

There is a decline in short-term memory and processing speed that is associated with middle age (here primarily defined from the 40s through 60s), but for most people it seems to be made up for by better intuition and expertise in life. So although one can't remember facts as well as one used to, problem-solving and wisdom skills increase to offset that, and reduce the need to remember facts quickly.

Also, contrary to the idea of "midlife crisis", most people are happiest in mid-life. The brain automatically focuses on the positive, lets the negative stuff go. The book explains some reasons this might be evolutionarily advantageous.

I recommend the book. It's a heartening anti-dote to our youth-obsessed media culture.