''Just living a plain, straight, ordinary, good life,'' Alma Ralston revealed yesterday.
''That's the only secret. You forget how old you are. When you get to my age, you go back and start again.''
More than 100 family and friends gathered at the Parklands Event Centre in Mosgiel yesterday to honour the family matriarch known as ''Aunty Alma''.
Relatives travelled from all around New Zealand and Townsville, Sydney and Melbourne in Australia for the celebration, her great-niece Yvonne Williams, of Gore, said.
Mrs Ralston (nee Turnbull) cut a chocolate birthday cake in front of a board covered with a century of old photographs of her and her late husband, Ivan.
She moved into the Birchleigh Rest Home in Mosgiel 10 years ago, after living most of her life in Allanton.
The party is not over yet for Mrs Ralston, who actually turns 100 today.
She is expecting ''a few visitors'' to pop in on her at Chatsford during the day. New Zealand has about 300 centenarians and about six people out of every 100,000 New Zealanders reach triple figures.
The oldest New Zealander is believed to be Maudie Wilson, who turned 110 on March 23 after living in Clyde for 75 years and now lives in an Invercargill rest-home.
