Sir Ian, chairman of the Wood Group and one of Scotland's best-known businessmen, will celebrate the double milestone tomorrow with a party at a country house outside Edinburgh.
In a rare concession, he has even taken Monday off work.
Sir Ian is looking forward to spending time with his family and advancing the work of its charitable trust, particularly in Africa, where he is investing in tea-growing communities.
After 30 years as chairman he will leave Wood Group's headquarters in Aberdeen for the last time on October 31.
Sir Ian, whose family has an estimated worth of around £1.2bn, has no regrets about his hugely successful but busy business life, which started when he went to work at the family fishing trawler businesses, founded by his grandfather in 1912, after graduation from Aberdeen University in 1964.
He had planned planned to become a doctor, partly to please his mother, but chose to do a psychology degree and keep his options open.
Telling his mother he was sticking with business was "one of the hardest interviews of his life" given she hoped her son would become a professional man.
Family is hugely important to Sir Ian, who has three sons with his wife Helen and six grandchildren, but is aware his job has been king for much of his life. Reports of working seven days a week are not exaggerated.
He said: "I like people who are committed and involved at work but family life is also important. I have chosen a slightly over-the-top approach to work but that's my style, that my nature. It's the nature of the beast.
"I have dedicated a lot of time to my work life and less time to my family, but that time has been real quality time. In that regard I don't have regrets. I have got a really understanding wife. She understands the nature of the person she married."
Sir Ian considers himself lucky to have been an ambitious young man in Aberdeen at a time when North Sea oil was being struck in the massive Brent and Forties fields.
He said: "I am of that generation that had the benefit of the emerging oil and gas industries. My father's generation didn't understand it and resented it a bit but I was in the right place and the right time. That was a stroke of luck."
The Wood Group, which provides engineering services and personnel to the oil and gas trade, employs 41,000 people in 50 countries and announced a 60% profits rise last year to £160m, with revenues rising to £3.8bn.
The luck Sir Ian speaks of also appears to be a burden on some level. He feels strongly about legacy and worries for the future of his home city which has boomed on a single industry.
He added: "Aberdeen doesn't have any kind of prosperity problem right now but what worries me most is just how we are dependent on one industry for that prosperity.
"Over time, given that it is a depleting industry, Aberdeen will face a challenge. Aberdeen has not had to compete in the last 20 to 30 years but we are going to have to compete in the future.
"My key message right now is we have got to enhance the infrastructure. The airport runway needs extended, we need the bypass and we have to do something about the city centre."
Sir Ian said he had "no interest in rich lists" when asked about his wealth. He said: "I am a Scot at heart and am careful with money, but I like value.
"I go on nice holidays and the family are going on safari and then to Mauritius. I would never buy a yacht, plane or villa abroad because there is no value in that.
"We have got a nice second home at Loch Tummel in Perthshire. I haven't got to it that much but my family love being there. If that's what you get for spending money, then I am quite happy with that."
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