• Khloé Kardashian said she tried to "close a lot of chapters" when she was 39.
• Kardashian, who turned 40 in June, called the process "shedding."
• Approaching midlife can be comparable to a second puberty, an expert previously told BI.

Khloé Kardashian prepared herself for her 40th birthday.

In an interview with Bustle published on Wednesday, "The Kardashians" star discussed her birthday milestone.

"When you're young, you think 40 is so old, and now I'm like, 'Wait — I feel so good!' said Kardashian, who turned 40 in June.

"I am in the best shape of my life. I'm doing new career stuff. I've only been 40 for about six months, but it's the absolute best. You don't give a shit about some of the stuff you once did," she added.

She said she intentionally "tried to close a lot of chapters" at 39.

"I called it shedding — shedding this decade of my 30s and this energy I wanted to leave behind," she said, adding that there are "so many new things" she's doing in her first year of being 40.

Turning 40 can be a daunting period. It's approaching midlife — a "biological regularity comparable to a second puberty," Hannes Schwandt, an associate professor of human development and social policy at Northwestern University, previously told BI.

"When you're young, you are typically overestimating what you're getting in the future," he continued. But not everything in life turns out the way we expect them to, and this can lead to disappointment, Schwandt said.

Aimee Pearcy previously wrote for BI that she felt disappointed when she hit the birthday milestone. "I always thought I'd be a millionaire by the time I turned 40, but here I was, living in a van, broke," she wrote.

However, she eventually came to terms with her age. "I realized that age is just a number," she wrote.

"Now that I'm in my 40s, I feel like my life is just beginning."

A representative for Kardashian did not immediately respond to a request for comment from Business Insider sent outside regular business hours.