Wanganui Collegiate School hosted the annual Big School Society Luncheon on Saturday.
There were 90 old boys in attendance and the most senior member was 99-year-old Philip Stewart of Amberley, near Christchurch.
Mr Stewart will celebrate his 100th birthday in three weeks.
The invitation-only luncheon was established in 2007 by headmaster Craig Considine and is restricted to past pupils who attended the school at least 50 years ago.
This year, the newest inductees to the invitation list are those who graduated in 1967, making them 68 years old.