"The more I drove through the town as I got older, the more I knew I had to come home and help our young people," he said.
"Money was going to all sorts of organisations and kids were still standing around."
As soon he hit pension age and was free of the need to earn a living out of town he started pursuing the idea in earnest, with the support of his wife, who was still working and happy to let him follow his dream.
"A man's got to get his dream in, some time in his life," he said.
He opened Te Mira, or The Mill, in December 2010, in what had been a pub. His goals were to improve the town's health and well-being, and offer rangatahi options other than gangs or "walking the streets causing trouble."
He also wanted to do it without government handouts, relying only on sponsorship and membership fees paid by adult users.
The Mill is free for kids from the age of 10 until they leave school.
"It has 550 users a month, two-thirds of whom are youth. It is also used by Corrections staff and police, who now rub shoulders with some of the youths they used to have trouble with.
"There were kids in here who'd cross the road when they saw a cop coming. Now they'll stop to talk. It's created a rapport," Mr Warren said.
"It's like a sanctuary in here. It's a place where everyone's equal."
Dedicated volunteers had made The Mill possible, including fitness trainer Ada Kire, youth worker Grant Komene and Trish Muldrock, a reigning world powerlifting champion in the 48kg class, he added.
He had drawn on his contacts to get sponsorship from Mt Pokaka Mill - "Half of their staff live in Kaikohe, so the company has a vested interest in looking after this town" - as well as Law North and Mainfreight, whose founder was a childhood friend.
"They all stepped into the ring, along with the landlord of this place, Mark Evans, who cut the rent right down," he said.
Initially it had been his goal to see The Mill survive - if it was still going in a year he would strive to achieve another year. When winter came he thought the kids would stop turning up, but they kept coming, and this year had been "absolutely marvellous."
The Mill is also used by schools in Kaikohe, especially Northland College, and Moerewa. A nutritionist and a dental hygienist visit for regular information sessions.
Mr Warren told last week's awards ceremony that nutritionist Tracy Ayton was making a real difference, particularly with girls. Some young netballers who were regular gym patrons had improved significantly under her guidance, although their male counterparts were more of a challenge.
"Boys eat anything," he said, "thinking they can just burn it off. The time will come though when burning it off will get harder."
Mr Warren, who competed in several world powerlifting championships, with his best ranking third in the world, and also trained the former Northland boxing star Mohammed Azzaoui, had some advice for the younger generation too.
"If you can't get a job, offer to work for someone for nothing," he said.
"If you're any good they'll keep you on."
Life was like boxing, he said. Everyone had to prove that they could throw a punch, take a punch, and at the end of the day walk away smiling.
All the winners - pages 7, 8.
