But he has kicked on in 2015, as it were, and heads to the nationals as the Auckland and North Island schools 1500m champion. His personal best stands at a rapid 3m 55s.
He broke the school's 1500m mark at the Auckland Grammar athletics day in February, which had stood for 30 years, and received congratulations from previous record-holder Philip Hill, who is now a professor at the University of Otago.
"It meant a lot to me because all my family and friends from the hostel came out and watched me as well," said Kilmister, who said breaking that record was a main goal.
It wasn't when he arrived at Auckland Grammar in 2011.
"I came here to be a rugby player," he said. "I'd made North Harbour Roller Mills.
"I'd never lost a school cross country race. I came here and came 42nd. I gave up running and it was my Year 10 athletics coach who got me back into it."
The rugby has since fallen away, but he still trains with Conal Wilson, Auckland Grammar's gun cross country exponent. He loves the 800m but admits his success in the 1500m has encouraged him to push on at that distance.
Kilmister says he has learned a lot under coach Bruce Jones, a former training partner of John Walker and Dick Quax, and a follower of the Lydiard philosophy of solid mileage to build up middle distance runners' ability to kick in the last 300m.
"He'll change trainings if I'm not enjoying it. I can have a day off if needed," said Kilmister, who still runs up to 100km a week.
Kilmister also learned a lot off 2014 Auckland Grammar athletics captain Michael Dawson, and imparts some of that knowledge to some junior runners he coaches.
Kilmister has undergone a mental transformation in his approach to competition over the past 12 months.
"I don't let other athletes' times get to me now," he said. "When I first started, I used to be really scared about what they'd done ... That happened last year. That lack of confidence meant silver."
Now he can relax more easily and is better at zoning in when he needs to.
Some time off over winter to catch up on his studies and social life means he is fresher now and building solidly towards the nationals in Timaru. His main competition is expected to come from the likes of Westlake's brilliant young Dan Hoy and Avondale's Luke Fielding.
Kilmister is a finalist in the ASB YSPOTY awards boys' athletics category, up against Liam Speer of Massey and Niven Longopoa of MAGS. That event falls a week before the nationals, but Kilmister's focus won't change.
One day he hopes to earn a running scholarship to an American university but in the medium term would love to break 3m 47s needed for 2016 world junior championships qualification. It's an achievable goal at his current rate of improvement.
It might be premature to say New Zealand has another Nick Willis on its hands, but Kilmister has the attitude, dedication and drive to succeed.
