Mr Macdonald (72) is still playing tennis year-round and is competing in a South Island tennis festival at the grass courts in Oamaru.
The festival, which finishes tomorrow, is an annual event for players aged 35 and older.
There was no upper age limit - "fortunately for me", Mr Macdonald laughed.
With 12 teams of eight, each comprising four men and four women, plus reserves, nearly 100 people are participating.
The competitive edge was apparent: "There's a bit of pride.
You never lose that will to win, I certainly don't think," Mr Macdonald, a retired farmer, said.
The tournament has been run for 16 years and Mr Macdonald has played in most events.
The best part of playing sport was the people he met.
He has been playing tennis regularly since he was about 8 and now plays twice a week, sometimes more, all year round.
Mr Macdonald has always been keen on sport, particularly tennis, rugby, hunting and fishing.
"Just a man's world really. . . and I love them all," he said.
He gave up playing rugby when he was 22 due to injury and took on refereeing.
He refereed rugby for more than 30 years.
He had no plans for retirement from tennis and would continue "as long as the body's willing".
He never suffered aches or pains, he said.
Once the festival finishes, Mr Macdonald and his wife, Aileen, will head to Haast with a boat and tent and "feed a few sandflies".
They will then head to Melbourne to watch the Australian Open later in the month.
"It's not a bad life," he said with a smile.
