Media playback is not supported on this device
The 62-year-old is going public about his condition to raise awareness about dementia.
"If I can help others talk more openly about dementia then that will be something positive," said Calderwood.
"I can have a moan, as many of my players would say, but I've had a wonderful life in football. I've seen great places, travelled the world."
Calderwood also managed Kilmarnock and Ross County, while he played and coached in the Netherlands after beginning his career at Birmingham City.
"It's strange, I can still remember the big moments like they were yesterday," he said. "You never forget them.
"Getting promotion with Dunfermline, saving Kilmarnock on the last day of the season.
"I got sacked for a couple of things I don't think I should have got sacked for. Aberdeen was the hardest one. We got back into Europe and the chairman decided to make a change. That still annoys me."
A faltering appearance as a TV pundit for last year's Scottish Cup semi-final between the Dons and Hibernian is a source of regret.
"I felt that wasn't right and I shouldn't have done that," he said. "I was really angry with myself."
By then Calderwood was aware of problems with short-term memory.
"It was probably two, two-and-a-half years ago that I started to notice it and it has got worse since then, forgetting things and such," he said.
"I was still putting myself forward for jobs.
"I knew I was ill but I was still going to watch football and you think you can do it.
"Who knows if that was the case or not? Eventually, I made the decision; the game's finished for me.
"But I enjoyed it all because I just love the game."
Former Aberdeen and Dunfermline manager Jimmy Calderwood has been diagnosed with early onset Alzheimer's disease.