Les Thomson is one of the last remaining World War II veterans in Australia.
He celebrated his 100th birthday at Doyalson RSL on Thursday with a large group of family and friends.
Son-in-law Graeme Marsh said "there's a real good chance he'll be the last World War II veteran in Australia".
"From what I've seen, he's going strong," Mr Marsh said.
Mr Thomson walked around the RSL with a walker and spoke well.
He joined the Australian Army in 1941 at age 18, fighting in New Guinea and Borneo with the 2/33rd Battalion.
He was a frontline soldier and "mortarman".
Mr Thomson's biographer, former Sun Herald editor Peter Allen, said "he was involved in very significant battles".
"He saw action in the campaign to recapture Lae from the Japanese," Mr Allen said.
"He also saw action in other famous battles, including the Markham Valley and Ramu Valley campaigns and the battle of Shaggy Ridge."
He witnessed a US Army Air Force Liberator bomber crash into a convoy of trucks carrying Australian troops at Port Moresby on September 7, 1943.
The crash claimed the lives of 73 men, including 60 Australian soldiers.
Soon after the incident, Mr Thompson entered another battle.
Asked about war, Mr Thomson said "I wouldn't recommend it to anyone".
"War is a terrible thing. Women and kids are getting killed now. That's disgraceful."
After the war, he became a painter and decorator and worked in that trade until retirement.
He grew up during the Great Depression.
"We used to live in Balmain. That's where I was born," he said.
"From there we moved to Marrickville. That's where I joined [the Australian Army]."
At the time, he said many people didn't own their home "as they couldn't afford it".
"We'd move from place to place and I didn't get much education. There weren't any rich kids, not where I was.
"We used to take our billy carts along the train line and pick up all the coal that would fall off the trains. We'd put it in the fire of a nighttime."
He did what he could to make some money as a youngster.
"Things were hard to come by. We used to go to the stables, collect manure and sell it for sixpence a bag."
Mr Thomson put himself in a nursing home at Norah Head only two weeks ago.
"It was his decision," daughter Anne Marsh said.
"He's already joined the committee."
Mrs Marsh is looking after her dad's 13-year-old fox terrier Jessie, but "she can go and visit him".
Her dad "still goes to the gym".
"He always kept active with gardening. He had bonsai trees. He helped us build our house."
Son Mark Thomson added "he liked to walk and still does".
Mr Marsh lost his wife Margaret in February at age 93. They were married for almost 75 years.
