"I was switched to backstroke when I was a teenager because I was never going to make the Manawatū team in freestyle," she says.
The retired teacher endorses the "fun, fitness and friendship" motto of New Zealand Masters Swimming.
"I like the social side as well as the fitness side."
Mills says the Makino Masters are "an amazing team", "a great group", with the swimmers going for morning tea afterwards.
Members range from their 40s to 80s with club coach Sara Kennard providing a varied programme. "She's our motivating force."
Mills swims three to four times a week, averaging 2km each session.
Mills' late husband, Kevin, used to manage aquatic centres and about 30 years ago the couple was part of the organising committee for the Masters Games in Whanganui.
Last year, Mills went to Dunedin to compete in her first South Island Masters Games.
"Masters is for everybody, not just those who want to be competitive swimmers. There is no need to belong to a team or a group."
With no qualifying times for the Masters Games, Mills says it does not matter how fast or slow a swimmer is and the emphasis is on enjoyment.
"It's a very encouraging sort of a sport," she says. "We just do it for the absolute fun of it because it is such a cool thing."
Mills is now a writer with one of her three published books, Down at the Baths, about the Palmerston North Municipal Baths that were in Ashley St. Mills used to swim and work there.
In March, she is competing in the Taranaki Masters Games.
Mills' goal is to still be swimming competitively aged 80.