The northern beaches may be in lockdown to help stop the spread of COVID-19, but this 104-year-old celebrated her birthday in fine style with cake, music and a few laughs on Monday.

Born on December 21,1916, Mrs Byrne is the oldest resident in her retirement village, Baldwin Living Seabeach Gardens.

When it comes to pandemics, health authorities might say COVID-19 is "a once-in-a-lifetime event", but Mrs Byrne has been there and done that and was actually born amid the Spanish Flu pandemic that ran from 1912-19.

During her lifetime she's also seen two world wars, the Great Depression and the Global Financial Crisis.

When she left school she became a high school teacher and her piano playing filled classrooms with music and joy.

"I started at a little school in Narrandera near Wagga," she said.

"My mother was very musical, she played piano and violin. She tried to teach me violin but I was hopeless."

Then, when she was 24 years old, she married her great love Kevin Byrne, it was 1940 and midway through the Second World War.

Once married rules meant that Mrs Byrne had to give up the job she loved.

"In those days you had to resign when you got married," she said. "But, I went back to teaching after the Second World War when lots of migrants came over to Australia."

Sport has long been a passion for Mrs Byrne, who until recently was still playing lawn bowls.

"I played basketball, tennis, golf. We're an outdoor country and most people do sport," she said.

Pat and Kevin went on to have four children, three girls and one boy.

While Kevin has since died, Mrs Byrne is now a grandmother to six, and a great grandmother to five children.

When asked what the secret to a long life was, Mrs Byrne said it was simple.

"It's good food and I didn't smoke and I might have a little sip of wine everyday," she said. "My advice is eat plenty of chocolate and do plenty of sport and get plenty of sleep."