This black-belt granny means business.

Rosemary Braithwaite has just become the first 72-year-old in New Zealand to reach her "shodan" black belt in Seido karate.

If it came to having to deal with would-be attackers, Mrs Braithwaite says she is sure she would know what to do.

"I expect that because I have been doing it for so long instinct would just kick in."

Mrs Braithwaite began karate 15 years ago, after she was taken by a friend to Nelson's World Seido Karate.

"I thought it was interesting and it was a nice group of people."

That group of people might have changed, but her commitment to study has grown. Mrs Braithwaite is now the oldest member of the dojo.

"It's a bit daunting, because if you're the oldest, you have to be something of a role model in terms of inspiring the younger ones.

"They can think it's something they can do for the rest of their lives."

The grandmother of nine said her grandchildren were all "quite chuffed" with her achievement.

"I think they are probably all quite surprised, but I'm sure they are all proud of me."

To achieve her black belt, Mrs Braithwaite had to undergo a three-hour grading, where she went over all the skills she had learned in the past 15 years before sparring with dozens of other black belts.

"Most (black belts) have to do 40 bouts, but because I'm over 70, they let me off with a little less. There are not too many good things about being older, but that's one of them."

Mrs Braithwaite said at the end it felt like a great success, and in the few weeks before the grading, she put in more than six hours a week at the dojo.

"You set yourself this challenge and when you decide to accept it, you have to go through with it and keep going until you have done it."

Mrs Braithwaite's teacher, Andy Barber, is one of the most senior members of Seido karate in New Zealand and the world.

He said her black belt dispelled the misconception that karate was just for young, tough people.

"Rosemary is an absolute star. She has been training and training without expectation, and she doesn't expect any favours. She gets out there and has never been judgmental about herself, and others have not been judgmental about her."

Mrs Braithwaite said it proved that age did not matter and she would continue to practise karate.

"If you really want to do something and are physically able, there is no reason you can't do it."

- © Fairfax NZ News