At 27, Douglas married Mary and they had three daughters and adopted an autistic son.
But the couple "tragically" divorced 37 years later. Then, aged 65, Douglas lived alone for the first time in his life. He described that period as a "challenge".
However, it was his midlife crisis at 50 that really tested Douglas' resilience. After years of alcoholism he knew he had to kick the habit. He ended up going into rehab for three years and weathering periods of depression and loneliness.
"Loneliness deteriorates into depression and depression is an extraordinarily serious state. It morphs into suicide.
"It got to the stage I wanted to stop the world, I'd like to get off. I've been there and done that, I wouldn't wish it on anyone.
"I fell apart and I needed very serious counselling and I realised that there were things I hadn't done in life that I would like to do. I had to find some activity that was challenging and worthwhile."
His local butcher invited Douglas to join him running marathons.
Now, almost 40 years later, he hasn't touched a drink and has nailed 29 full marathons. This May he has plans to crack his 50th half-marathon in Rotorua. Training consists of four walks a week including one 16km trek with the marathon club on Sunday mornings. He also does two weekly weights sessions and one aqua jogging session.
Last year he entered the World Masters Games and won a bronze, two silvers and a gold for the 10km road race.
Keeping busy meant he enjoyed his solitude and didn't find it lonely, Douglas said. He believed seniors had to take more responsibility for connecting themselves with their community.
Being as active as possible was key.
"The world doesn't come to you. You've got to go out to the world. You have to make that effort.
"If you get lonely you have to get off your butt and do something about it.
"Loneliness is restrictive. The world narrows and [lonely people] become more inwardly directed and inactive. They isolate themselves. It's deteriorative, I think they lose and society loses because of their inactivity."
The YMCA's inverted triangle idea that stands for mind, body and spirit resounded with Douglas. He believed if you keep your body fit, your mind and spirit would follow.
Running has been crucial to turning Douglas' life around and keeping it on the right track. It gave him something to focus on, as well as camaraderie and support.
"I'm very strong on self motivation. It comes from within.
"Running has been my saviour."
