Feeling apologetic, Mr Richardson offered to walk her home, but persuading her to agree wasn't easy, he said.
She had come to the dance with another boy and had felt "terrible" about leaving with Mr Richardson, so they decided to sneak out the back of the hall without the other boy seeing them. "It all went from there," Mr Richardson said.
The couple married in their hometown before moving to New Zealand and lived in Wellington for about 30 years and in Rotorua for the last 20 years.
Mr Richardson, 89, said the secret to their long and "very happy" marriage was that there were no secrets.
"We're always honest with each other, we do everything together."
There was also a rule that they would not argue over two things. One being religion, as they had been brought up in different faiths. The other, money.
"We argue over just about everything else," Mrs Richardson, 90, said.
On Monday the couple celebrated their anniversary by going out to dinner with close family and friends.
They have a daughter, two grandchildren and two great grandchildren.
The couple received congratulatory letters from Queen Elizabeth, Prime Minister John Key, the Governor General Sir Jerry Mateparae, Rotorua MP Todd McClay and others.