His great-grandkids were screeching in the den, one grandkid clamoured to be heard over the next and a small dog yapped shrilly. But when Mohammad Mohyeddin raised his finger and began to answer the question — what’s the secret to long life and good health? — the gaggle fell silent.

“Be truthful,” his daughter Parvin translated as Mohyeddin held forth in Farsi. “I never said a lie in my life.”

“I have a clear conscience. So I sleep well.”

Mohyeddin, a general under the Shah of Iran, a husband of 75 years, a father to eight children, and grandfather to 20, turned 105 years old on Saturday. His advice — summarized neatly by the Zoroastrian axiom “good thoughts, good words, good deeds,” which the family had minted on the reverse of a coin bearing the profiles of Mohyeddin and his wife Ashraf — is only the beginning of what the sharp centenarian had to say about living life well. For the occasion, he wrote out a letter containing all his accumulated wisdom.

Always drink pure water, eat food that comes from the ground — not from a package — and chew carefully, he says. Actually, Mohyeddin is pretty specific about the food part: Don’t eat pickles or anything else brined in salt. Sausages are out too. Eat fruits and vegetables. He always eats an apple before breakfast. He doesn’t drink or smoke, and has no problem lecturing a stranger on quitting tobacco.

Exercise. Choose a spouse who will be a true companion. And take care of family first. “It’s the love of them that gives me power to live,” he says, gesturing to the clan crowded around him.

Mohyeddin was born in Tafresh, Iran, in 1906. He rose through the ranks of the Shah’s army, until he became a high-ranking general. In 1979, during his visit to a daughter in Montreal, 80 generals were killed in the revolution. The family promptly relocated to Canada.

In the years since, Mohyeddin has enjoyed a peaceful retirement, keeping abreast of the news and never hesitating to send a sharply written letter of advice to a newspaper and even a world leader.

As it happens, this year marks his 75th wedding anniversary. Ashraf has some thoughts on that part of life too. “Compromise,” is one of her mantras. Give to one another. Have lots of people coming and going, so you’re not stuck with the same person all the time.

As a mother, be honest with your children. “Try to be their friend, even though you discipline them,” her granddaughter translates. And educate them well, above all.

“I gave everything I had to my children and family,” she says. “And it’s worth it in the end.”