His hearing, albeit with an electronic aid, is sharper than that of people decades younger and his face is almost devoid of wrinkles, except when he smiles, which is often.
He lives in his own home, walks without an aid, drives his own car, plays bowls and attends horse racing meetings.
He has three children over the age of 70, another aged 65 and, despite his youthful appearance, turns 100 today.
Mr Weir said he met Mr Robertson, of Alexandra, 10 years ago when he responded to an advert Mr Weir had placed in the paper, calling for expressions of interest in joining a harness race horse-owning syndicate.
He checked a form Mr Robertson had filled out and saw his date of birth.
''I said 'look Toby, I think there's been a mistake' ... he was 90 then and he looked 70; he still looks 70 now ... he's an amazing man.''
Mr Robertson was born and bred in Dunedin, the youngest of four children, to two Scottish immigrants, John and Louisa.
His father was a linotype operator at the Otago Daily Times until he moved to Australia with second wife Jessie in 1931.
Louisa had died in 1923.
Mr Robertson has only had two jobs in his life, and devoted 30 years to each.
The first was as a warehouse man for a wholesale company and the second as branch manager for a small warehouse company, which was owned by a larger Wellington-based company.
A few years into his first job he met Margaret ''Rita'' Davie, ''at some party ... somewhere, I suppose''.
They were married in 1938 and had four children - Noeleen, Joan, John and Stephen.
The only significant time he took off work was during World War 2, when he served in the air force ground staff for two and a-half years.
Mr Roberston moved to Central Otago after retiring in 1989, first to Clyde then to Alexandra, after Mrs Robertson died in 1992.
Since retiring, he has kept himself busy with sport - ''I love sport''.
He regularly played golf, until his legs got too bad a few years ago. He still plays bowls, though, usually at the Alexandra RSA club and also at the Alexandra club.
He also watches his horses race as often as he can. As well as the trotting syndicate, he also belongs to a galloping one. Betting on horses is one of the highlights.
''My main bet is $1 to win and $2 to place, so I'll never go broke doing that.''
On turning 100, he said ''that's just the luck of the game'' but later added, ''genes have got something to do with it'' and ''everything in moderation is the story''.
He celebrated with almost 100 friends and family, including some of his 11 grandchildren, 22 great-grandchildren and three great-great-grandchildren, in Alexandra on Saturday evening.
