I am turning 80 today, my first day as an octogenarian. It is encouraging to report that I’ve arrived at this mortal mile marker relatively unscathed by the ravages of time. I had a broken arm in my youth and a broken heart five years ago that was mended masterfully by cardiac surgeon Betty Kim at Penrose Hospital.

“Around the turn of the 20th century, life expectancy was about 50 years, and people who lived longer than that often did so with chronic physical and mental ailments. Now, the average life span is into the 80s,” said Lewis Lipsitz, M.D.., chief of the Division of Gerontology at Beth Israel Deaconess Medical Center and professor of medicine at Harvard Medical School, “and many more octogenarians remain cognitively and physically vigorous, experiencing most if not all of their old age without disease or disability.

“Seeing people living long and successful lives used to be the exception, and it’s becoming the rule today. It’s what we call the ‘squaring of the survival curve.”

Squaring the survival cure and arriving at 80 is a significant way station. If you are fortunate to reach this port in life’s storm, it is a time to look backward and forward, as I have, and give abundant thanks for the privilege.

I have an overriding sense of gratitude for experiencing such a long and lucky run at life, past and present, notably, my wife of 55 years, Shirley, and our son, Hascy II, who arrived at Sandborn Western Camp at age 10 and attended Colorado College, where he met his future wife, Jennifer, and our adolescent grandson, Ember.

The flip side of slouching into my ninth decade is being aware that the grains of sand at the bottom bulb of life’s hourglass far exceed those in the top bulb. Nor do I enjoy being required to play mortal musical chairs with my peers. On the contrary, every “victory” is a painful loss in this zero-sum game.

Eighty years of age is an unalterable chronological fact. It is also an alterable state of mind. One might feel and act like a living antique and lament, in the words of the song “Get Up and Go,” popularized by Pete Seeger: “How do I know my youth is all spent? My got up and go has got up and went.” Or one can be sanguine, remaining young in head and heart, if not in body.

One tonic I’ve discovered for keeping a fresh, optimistic look at life is sharing it through the eyes of the youth: Since moving here eight years ago, I have dedicated time and enthusiasm to working with the young —from preschoolers to high schoolers — in Colorado Springs classrooms.

My birthday falls on the United Nations’ International Day of Tolerance, a celebration championing mutual understanding and respect among nations and peoples worldwide. After enduring months of vituperative national and local campaigning for political office, it is a particularly significant occasion for our country.

Eighty years—29,220 days—on this planet have afforded me a greater understanding of myself and the world around me. An avalanche of life experiences has taught me many joyful and harrowing lessons. One of life’s final exams, which I have been cramming for with increasing fortitude lately, is being ever more empathic and tolerant of the foibles of others in our increasingly intolerant age.

Todd Tarbox, author of several books including “Orson Welles and Roger Hill: A Friendship in Three Acts,” lives in Colorado Springs.