"I freaked out two months before I turned 40, not knowing that that age would even mean anything to me, but then it's, like, oh but, 41, 42," Simpson said during SiriusXM’s "The Jess Cagle Show" on Thursday.
"I’ve never calculated my age until now," she continued before adding with a laugh: "I am accepting it slowly."
NEW YORK, NEW YORK – FEBRUARY 04: Jessica Simpson signs copies of her new book "Open Book" at Barnes & Noble Union Square on February 04, 2020 in New York City. (Photo by Kevin Mazur/Getty Images) (Getty)
The mom of three went on to explain that she's someone who "reminisces."
"I hold on to so many memories," she said. "I am so tragically romantic like that about my own self … Thank God I put a memoir out at 40 because it would have been 800 pages if I waited any longer," Simpson added, referencing her book, "Open Book."
To mark her birthday, which was on July 10, she shared a photo of herself fitting into jeans she's had since her 20s.
In the Instagram pic, Simpson is seen in a hoodie and light wash distressed jeans.
“I have kept these throwback True Religion jeans in my closet for 14 yrs (I’m not exaggerating!),” she captioned the mirror selfie.
Of the photo, Simpson said during the SiriusXM podcast on Thursday: "That was like a really random thing. Because I haven’t put jeans on through the whole time, I've been in sweats. I am, like, embracing the quarantine life."