1.  Live Longer
A recent report analyzing the data from nine studies revealed a strong correlation between walking pace and expected survival rates for folks over 65.  Start walking young so you will keep your fast gait as you age.  Slowing down as you age means your body can't maintain the oxygen level it needs for brisk walking.
Tip:  start walking briskly now, no matter your age.
 
2.  Dementia
Walk six miles a day and prevent brain shrinkage and dementia.  The 300 people in this Pittsburgh study showed that those who walked at least 6 miles a day had less age-related brain shrinkage than those who walked less.
 
3.  Battle Breast Cancer
The Archives of Internal Medicine recently published a study showing a 15% reduction in the likelihood of getting breast cancer for those women who walked briskly for 1 hr a day.
 
4.  Protect Your Prostate
The Journal of Urology is 2009, published a study that showed that men who underwent biopsies for prostate cancer suspicion were 2/3 less likely to be diagnosed with the disease if they exercised the equivalent of 3 or more hours a week.  
 
5.  Slash Your Stroke Risk
A study of 39,000 healthy women 45 and older who walked more than 2 hrs per week were 30% less apt to have a stroke than those who were sedentary.
 
6.  Soothe Your Tummy
Move regularly and calm an irritated bowel.  In a study of adults with Irritable Bowel Syndrome, 43% who walked briskly 3 - 5x a week showed significant improvement in their symptoms of cramps, diarrhea, bloating and constipation.  Walking is healthy for the entire digestive system.

 
conclusion:  Start walking, keep walking, don't stop walking!  And do it with a friend so that you can solve all of the world's problems at the same time!