The worst thing you can do as you get older is nothing. Sitting and not moving, such as when you watch TV or surf the internet, is your enemy. Your body and mind need exercise, or else they will both turn to mush. It will happen more quickly than you think.
Go ahead and watch that football game or that movie, but every half hour, stand up, stretch your arms and legs, twist your torso, march in place for a few seconds, maybe take a lap around the house, or go get the mail, put a load of laundry into the washer. Just do something that requires moving. It wakes up your heart and lungs and improves your blood flow.
At least once each day, make your brain work a little. Read a book, do a crossword puzzle, figure out your budget, work a jigsaw puzzle, just something that makes you think.
Move it or lose it. It really is true.