The two stayed in touch, writing to each other and spending weekends together.
"When we were 18, we decided to get engaged. We got married the following year."
The ceremony was held at All Saints' Church on Duncan St and the reception was at the former Wanganui Savage Club.
"Everything was such a whirlwind. I remember coming out of the chapel and getting heaps of photos taken.
"It was a funny time of the day. Why we picked 11.30 in the morning, I'm not really sure why."
Family members weren't so sure if it was a good idea to get married at such a young age. The Nat King Cole song, Too Young, was played at the wedding as a bit of a prod to the claim. To this day, the song still brings a smile to the pairs' faces.
"I had an aunty that said I was far too young to get married. Of course, every time that song comes on we do a bit of a giggle to ourselves."
After spending five years in Lower Hutt, they moved to Valerie's home town of Whanganui. They've lived on Moana and Hinemoa Sts over the years, before settling into their Burton Ave home. Valerie still lives there some 49 years later.
"We have always lived in Whanganui East."
The couple have both been Rangatiras (president) at the Savage Club over the years, a place they spent many weekends.
"Alan had quite a good voice on him, he use to get up on stage and sing.
"To start it was men's only. I was one of the first women to be made a member of the club."
Alan had a stroke in 2017, paralysing half of his body. It was decided then it was best to admit him to a rest home to receive the round the clock care he needed. He has been in Kowhainui Home since.
Valerie goes up to see Alan each and every day.
Due to Covid-19 safety precautions and rules at Kowhainui, the pair won't get to spend the day the way they would have liked.
Only one person per resident can visit each day, meaning only Valerie can come in and see him for the celebration.
"We were hoping to come in have a bit of a morning tea, but unfortunately we can't," said daughter Linda Green.
"We wanted to come in and give him a big hug and tell him how proud we are of what him and mum have done."
Valerie plans on going up for the morning, with the rest of the family tuning in via FaceTime.
"It's just one of those things, unfortunately."
They were surprised and delighted to receive a number of letters over the last week, from Whanganui MP Steph Lewis to the Queen Majesty herself, congratulating the couple on their achievement.
When asked about what the secret has been to their kinship, Valerie shrugged her shoulders.
"I really don't know. We have always just had a great love for one another. When we have gone out, we have always done things together. We have always shared experiences."
The Watson's have four children - two daughters and two sons, as well as 13 grandchildren and eight great-grandchildren.