A study showed that people who exercise vigorously for around 3 hours a week had DNA and cells that were 9 years younger than nonexercisers. Three hours a week is a little more than 30 minutes a day.
Forget the study, though. What I know (from personal experience and from observing others) is that if you go more than 2 days without exercising, you are at a grave danger of quitting your routine. Somehow it is way too easy to slip from three days of nonexercise to three weeks of nonexercise to three months of nonexercise. The easiest way to create an exercise habit is daily repetition. When you promise yourself to exercise daily, you may skip a day but then get back on the program the following day. If you are exercising three times a week and, say, skip Friday, then you would have gone from Wednesday to Monday without exercising - a total of 4 days with no exercise (very dangerous, from a habit-building perspective). For life expectancy, it is more important that you exercise year after year than go through fits and starts of intense exercise followed by no exercise.
The other reason I feel that daily exercise is important, is that daily exercise will help improve your sleep and your energy level. It is important to just rev up your whole body each day. Remember, daily exercise doesn't have to mean going to the gym every day. Home exercises, such as yoga, stretching, free weights and more, can be incredibly effective.
Read More: The Hidden Benefits of Exercise