Sam and Bill's amazing adventure

Sam Olley, 21, and her grandfather, Bill Macalister, 82. Photo / Supplied

Most young Kiwis wouldn't pick an 82-year-old to travel abroad with. But Sam Olley, 21, didn't hesitate when her "young-at-heart" grandfather invited her on the Southeast Asia trip he'd hoped to share with his late wife.

Retired Central Otago farmer Bill Macalister and his wife, Shirley, had to cancel the trip they'd planned 10 years ago when she developed throat cancer. She died in 2014.

Losing his wife of 55 years was tough, but Macalister, whose mother lived to 99, hasn't slowed down. Committed to living life to the fullest, he decided to enlist his "best mate", Olley, to do the 16-day trip.

Their travels began on July 9 with five days in Vietnam's Ho Chi Min City before a Mekong River cruise. Their trip ends in Siem Reap in Cambodia.

"We're not really like granddad and granddaughter," Olley said. "We're more like really close friends. He sometimes calls me his best mate.

"We both love sport and history, we're both quite extroverted, and we have the same sense of humour.

Bill Macalister and Sam Olley started their shared jaunt in Ho Chi Min City.

"He's always been quite there and ahead of his times - he worked in London and travelled around Europe on motorbikes with his friend in the 1950s before anyone really did OEs, and almost all my earliest memories of him are of him doing slightly crazy things like shooting rabbits out the kitchen window."

Macalister has a cane to support his hip replacement, but insists on walking lots, carrying their daypack and getting in his 30-minute daily swim where possible.

"Half the fun is just watching him enjoying himself," Olley said.

"He keeps saying he's a 'box of birds' and talking about how chuffed he is because he couldn't have done the trip without me. Mum tells me I'm not here to party, I'm here to keep an eye on him, but he tells me to not worry about him, and have fun."

Olley, a Christchurch broadcasting student and part-time caregiver, realised some might find the duo's trip odd, but said those they knew understood.

Asked how he found travelling with his granddaughter, Macalister said he was "happy as a sandboy".