But Goodall was not wholeheartedly celebrating the milestone this month in Perth, Australia. The botanist and ecologist, who is thought to be the country’s oldest scientist, said that he has lived too long. And now, he said, he is ready to die.

“I greatly regret having reached that age. I would much prefer to be 20 or 30 years younger,” he told the Australian Broadcasting Corp.

When asked whether he had a nice birthday, he said: “No, I’m not happy. I want to die. … It’s not sad, particularly. What is sad is if one is prevented.”

“My feeling is that an old person like myself should have full citizenship rights, including the right of assisted suicide.”

Goodall was set to travel more than 13,000km this week to Switzerland. That country, like most others, has not passed legislation legalising assisted suicide, but under some circumstances its laws do not forbid it.

It’s there, in Basel, a city in northwestern Switzerland near the French and German borders, where Goodall plans to die.

For the past two decades, Goodall has been a member of Exit International, a non-profit organisation based in Australia that advocates for the legalisation of euthanasia, according to the group’s website.

Exit’s founder, Philip Nitschke, said on a GoFundMe page for Goodall that the group’s West Australian coordinator would accompany him to Basel.

“Once one is past the stage of middle life, one has paid back to society the debts that have been paid out,” Goodall said.

“One should be free to use the rest of his life as one chooses. If one chooses to kill oneself, then that’s fair enough. I don’t think anyone else should interfere.”

Swiss law prohibits assisted suicide, but only for “selfish motives”.

Goodall does not have a terminal illness.

In fact, until recent years, he appeared to be in good health – he played tennis until he was 90, he performed in amateur stage plays until his eyesight began to decline, and he kept up his work as an honorary research assistant at Edith Cowan University in Perth.

Goodall made headlines in 2016 when, aged 102, his university ordered him to vacate his office, saying he was a safety risk to himself. He challenged the decision and, with widespread public support it was reversed.

But Goodall said his health was declining.

He said that several months ago he fell down in his flat in Perth and, for two days, he lay on the floor until his housekeeper found him.

“I called out, but no one could hear me,” he said.

Goodall has made repeated unsuccessful attempts to kill himself in the past 12 months.

He said he believed it was time for him to die, but his country’s new legislation is of no use to him because it applies only to those who are terminally ill.

He said dying was part of life.

“Why should it make me sad?” Goodall recently said about his intended death.

“I don’t regard it as grim, I regard it as natural.”

Additional reporting by Associated Press