David Goodall (R) poses with Carol O'Neill of Exit International, which advocates for voluntary euthanasia, in Perth. Goodall, Australia's oldest scientist, wearing a top labelled "ageing disgracefully", has left the country for Switzerland to end his life at the age of 104, saying he is resentful that he must go overseas to die. Photo: AFP/Getty Images

A 104-year-old man left Australia for Switzerland this week to end his life, saying he regrets living until the age of 104.

David Goodall, a botanist and ecologist, wore a top labelled "ageing disgracefully" as he arrived at Perth airport for his flight to Switzerland, which has allowed assisted suicide since 1942.

He has an appointment with assisted dying agency Life Circle in Basel, Switzerland.

He got on a plane in Perth last night and bid goodbye to his family and friends.

"I should be glad when I get on the plane - so far, so good," he told 9 News.

"I have some of my family here - there are three grandsons here, I believe and my daughter Karen... It's very good that they shall be here to see me off".

He told ABC: "I am 104 years old so I haven't got much time left anyway. I might as well not have (my health) getting worse and worse, making me unhappy as it goes."

Mr Goodall will spend several days with other family in Bordeaux, France, before travelling to Switzerland where he is due to end his life on May 10.

'I don't want to go to Switzerland, though it's a nice country,' he told 9 News. "But I have to do that in order to get the opportunity of suicide which the Australian system does not permit. I feel very resentful."

When Dr Goodall suffered a serious fall in his apartment last month, he was not found for two days. Doctors said he needed 24-hour care in his home or to be moved into a nursing home.

This incident hastened his decision to end his life.

Last year in Australia, assisted dying was legalised by the state of Victoria after a contentious debate, but eligibility requires a person be terminally ill.

Dr Goodall told ABC last month: "I greatly regret having reached that age."

"I'm not happy. I want to die. It's not sad particularly. What is sad is if one is prevented."

During his career, Dr Goodall edited a 30-volume book series called Ecosystems of the World and he was made a Member of the Order of Australia for his extensive work.

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