Some might have none, he asserts, and he has had two. But that's quite enough for an 81-year-old, he says - eyes twinkling - this week.
While he considers age may now be a barrier to producing more books, it's not as far as skiing is concerned.
He did that the day before this week's launch of Snow Business so he could be sure he still knew what he was talking about at Thursday night's function, he says.
And it seems he did know what he was talking about.
At the launch, by publisher Longacre Press, at least 49 books were sold, slightly more than the 45 people who attended.
Mr Markby was thrilled by the positive reception and hopes more people will pick up his 60-year history of New Zealand's ski industry.
Up to 1200 copies of his first book, Garden Plants for Central Otago (2005), have sold and it is still selling strongly in Wanaka's PaperPlus store, so Mr Markby hopes his second book will appeal to readers, too.
The secret to success is to only write about things you know, he says.
"I'm going to quit while I'm winning.
"The point I would like to make is you've got to be an octogenarian in order to write that book. You have to have 60 years of experience . . . and you still have to have your marbles."
When Longacre Press said "yes" to his second book, he went to work from the very beginning - 1945 - when the ski "industry" was run by clubs and there were no commercial resorts.
Mr Markby became fascinated by the development of New Zealand's ski resorts as he delved into the history of the Mt Cook Tourism Company and ski industry pioneers.
Friends and contacts lent him photographs to augment his own and more than half of the 200 pages are filled with pictures.
The text covers skifields in the South and North islands and ends with Mr Markby's reflections on the snowboarding revolution, the patterns of change and the thrill of watching extreme skiers and youth seeking out new challenges and frontiers.
"Looking back over my 60-plus years of skiing provides a wonderful vista . . . That simple, challenging life has gone forever but we are all the hardier and richer for it," he writes.
Mr Markby was born in Oamaru and his family moved to Dunedin when he was young.
He was educated at Otago Boys High School, where his English teacher, Monty McClimont, influenced his love for language, literature and writing.
He was introduced to the outdoors by the scout movement and later joined the Otago Tramping Club.
He began skiing on home-made wooden skis when he was about 20, on the Rock and Pillar Range near Middlemarch. When Coronet Peak's resort opened in 1947, he started going there.
One had to be terribly keen to ski in 1945 because the equipment was terrible but when Coronet Peak opened, skiers finally began getting tuition, he says.
In 1968, Mr Markby became a founder member of the Treble Cone skifield and later joined the board of directors.
The prime movers behind Treble Cone - Rod Aubrey, Ray Cleland and Murray Raffills - were passionate about the mountain and Mr Markby enjoyed his seven years on the board. At that time, he was working in partnership in Dunedin with Gordon McLaren. The metal working company they founded, Metalon, is still operating in Dunedin today.
When Mr Markby retired to Wanaka 18 years ago, he continued to combine his love for skiing in Otago with trips to North American skifields.
He also began learning conversational German for pleasure, writing for magazines and spent an enormous amount of time in his garden, eventually writing his first book, a reference manual of suitable plants for the Central Otago conditions.
His wife Judith had been a tremendous help and guide during the writing process, he says.
"If she said she didn't like it, I accepted it."
