Take a course in computer. Use the internet to update and read more and more on line.
Use the Google Dictionary and update yourselve each day.
Use your memory and remember your past-time, the good things in your early life....
It works.
Read newspapers and watch the news to maintain an interest in what's going on in the world, and do sudoku puzzles and crosswords to keep the little grey cells oiled.
Take an Open University Course, signing up for a BA (Hons) in case you want to continue. It does wonders for morale, the mind, the memory (with magnesium of course) and getting one up in the morning. I got my first degree at 56 and 2 more since. It is my all time favourite pastime.