"This will be it. The machine's getting a bit worn out. It's getting slower and slower," he quips. Wife Betty is relieved: "I get tired just watching him."
So far, four of Thorne's family members have signed up to join him in the marathon, which he's chuffed about, and he's looking forward to the big cheering crowds which usually gather there. At the finish he doesn't expect any fuss, just to feel "good". He jokes he'll be glad to see the back of the 42.2km race "because it's a long way".
It will be the 22nd time Thorne has run the Rotorua event, which he reckons is this country's toughest marathon due to its hilly course.
He's part of the "Survivors Club" - those who have completed it 15 times or more.
He expects to do the Bay of Plenty course in six-and-a-half-hours. "It's about getting to the end, not where you come."
The only problem he has had along the way was when he required a knee replacement six years ago. A doctor mentioned he should stop running but Thorne carried on.
He counts the marathon in New Plymouth as his best because that's where he clocked his fastest time (3h 18m 38s) aged 69. But that same event provided his worst marathon experience too - he fell, had a difficult finish and later "had my eye stitched up".
But the New York Marathon was his most memorable because he ran it last year with his daughter and because "of the atmosphere" - he was among 47,000 runners who were cheered on by a crowd of millions. He was also the oldest runner there and got a fair bit of attention.
Asked his secret to being so fit at such an impressive age, Thorne says it's about eating well, not smoking, rarely drinking alcohol and training every day but Sunday.
He either runs, goes to the gym or water-jogs. He follows a special ritual too; eating fish and chips the night before every race.
However, Thorne will still keep on running half marathons. He's run 93 of these and will aim for 100 some time down the track.
Meanwhile, Athletics New Zealand spokesman Carl Jackson says the Rotorua marathon is proving "hugely popular" with 2300 runners already entered and 1200 entrants running shorter distances. A third of the entrants are from Auckland so far, while 140 are from overseas.
