How much exercise is "enough" for us Seniors?

Dear GAA Friend,

Do you wonder exactly what you should be doing to "stay fit" as you -- and I -- get older day by day?  I thought I was doing enough by going to the local gym about three times a week.  "To do what?" you might ask.  Well, I do a few stretches and un-kink my back on a foam roller. . . and
glance around to see what the young folks are doing. . . . Some, like "Spaghetti Man," surely could make a living in the circus: he is flexible beyond belief, rolling himself up in a knot and then standing on his head. Impossible!  I take myself to the treadmill, set the pace at about 3 miles per hour and start walking for 30 minutes.  If everything goes right, I log 90 minutes per week.  But is this enough to stay fit?  I consulted this excellent article from the World Health Organization to find out the facts.  Check it out--  http://www.who.int/dietphysicalactivity/physical-activity-recommendations-65years.pdf

Please share your ideas and practice about exercising and have a good week,  Susanne Paul for Global Action on Aging