90th Birthday Queen Jane Goodall Lives in Childhood Home with Sister When She’s Not 'Busier Than Ever' Spreading Hope (Exclusive)

“To be honest, I don’t feel any different from how I was last year at this time,” the legendary conservationist tells PEOPLE in this week's issue

Dr. Jane Goodall turns 90 today!

The legendary conservationist is planning to celebrate her milestone birthday at a number of celebrations, including one in New York City on Wednesday, with a guest list that includes Jon Stewart. Even Dave Matthews played at a private party for her last week in San Francisco. "I can't keep up with all these people in all these places!" she tells PEOPLE in this week’s issue.

But the beloved ethologist, who broke new ground with her trailblazing research on chimpanzees starting at age 26, doesn’t understand all the fuss about her birthday. “To be honest, I don’t feel any different from how I was last year at this time,” she tells PEOPLE.

On Monday night, Goodall spoke about her mission to protect the natural world at Manhattan’s Beacon Theater, where she received two standing ovations — and a rousing rendition of "Happy Birthday" sung to her by the audience.

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Jogging a few steps across the stage, she declared, to the audience’s great delight, “I’m still fit!"

As the audience at the sold-out event clapped and cheered, Goodall, in her characteristically humble manner, attributed her never-ending vigor to “good genes." Thanking her mother and father, she said, "I’ve been very lucky.”

She talked about how fortunate she has been in her career, starting with the unorthodox path she took to get to Africa. There, she earned the opportunity to study chimpanzees in their natural habitat at Tanzania’s Gombe National Park in 1960.

Related: Jane Goodall Gets Rockstar Welcome at LA's Apple Tower Theater — and Urges Climate Action: 'We're Not Invincible'

That October, she became the first person ever to observe chimpanzees making and using tools — something that scientists thought only humans could do.

She spent the next twenty years in Gombe, earning her Ph.D. in 1966 at Cambridge. In 1977, she founded the Jane Goodall Institute, a non-profit wildlife and environmental conservation organization.

She says she planned to stay in Gombe “forever” until she went to a primatology conference in 1986 that changed the course of her life. “I left as an activist,” she says.

Related: Jimmy Fallon to Plant a Tree for Dr. Jane Goodall for Her 'Trees for Jane' Campaign

At the conference, she learned how quickly forests were being destroyed, killing chimpanzees and other animals, which also made it difficult for the people who live in these areas to survive.

She was shocked when she learned chimpanzees were being used for biomedical research, "held captive in five-by-five-foot cages alone for decades," she says. Calling her visits to these facilities “some of the worst times in my life,” she worked hard with animal welfare groups to free the chimpanzees.

“Finally, about eight years ago, the last chimpanzees of the 400 that were being used for experiments," she says, were released into sanctuaries.

Little Down Time

These days, Goodall spends about 300 days a year traveling and spreading her message of hope, focusing her talks on conserving the natural world and fighting the climate crisis.

“I’m busier than ever,” she tells PEOPLE. “I feel that I was put on this planet with a mission.”

When Goodall isn't traveling, she lives with her sister, Judy Goodall, 86, in their childhood home on the south coast of England.

“It’s the house where we grew up,” she says. “We still have it as a family home. My sister lives there permanently. She's four years younger than me, but our birthday is on the same day.”

Related: Jane Goodall Sets the Record Straight on Her Friendship with Prince Harry and Meghan Markle

At home, Goodall says she still likes to explore the same garden she did as a 10-year-old girl, when she would sit in her favorite tree and read Tarzan of the Apes, one of her favorite books.

She likes to say she fell in love with the king of the jungle, “who married the wrong Jane.”

Much More To Do

Considering the state of the world and how the climate crisis is worsening, bringing with it destructive floods, droughts and hurricanes, she says she is working harder than ever to try to save the planet and encourage people to take action.

“We do have a window of time, but unless we get together and take action, it will be too late,” she says.

In February, she announced that the Jane Goodall Institute had teamed up with the Bezos Earth Fund to protect forests and biodiversity in the Democratic Republic of the Congo and the Republic of the Congo, a region that is key to helping slow climate change.

She will also continue to work with the Jane Goodall Institute's popular Roots & Shoots program, which encourages young people in 70 countries to care for the earth.

“We depend on the natural world for everything,” she says. “It’s like a beautiful tapestry, and all the threads are interconnected. As each species vanishes from this ecosystem, eventually it will collapse.

"So we must give young people hope," she adds.

On her birthday, fans are encouraged to do good in Goodall's name.

"Make waves to celebrate her birthday in a big way with #GoodAllDay!" the JGI said on Instagram."Plan to do a kind deed, embodying Jane’s spirit of compassion and activism. 🌿 Whether it’s planting a tree, helping animals, or spreading joy in your community, let’s honor Jane’s legacy by making the world a better place, one act of kindness at a time! 🌍 Every individual can make a difference!"

Click here to donate to the Jane Goodall Institute to help her protect the planet.

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