(7-18) The Phys Ed column in today's New York Times includes a good summary of recent research by Dallas exercise physiologist Ben Levine. (His wife happens to be a lifetime runner.) https://www.nytimes.com/2018/07/25/well/exercise-makes-the-aging-heart-more-youthful.html
The basic conclusion: A lifetime of regular moderate to vigorous exercise, like 4 or 5 times a week, pays big heart dividends in later life. In particular, it increases arterial elasticity--the opposite of stiff arteries.
Individuals who exercise regularly through midlife get the biggest payoff in later life. But there are fitness benefits even for those who are sedentary for much of their life before beginning a regular exercise program. In other words, it's never too late to start.
Levine also draws a distinction between a couple of leisurely walks a week and four to five real workouts. The former might not get the job done. Try to exercise on more days per week than you don't exercise.
Here are links to Levine's studies in PubMed: