Jennie Garth 'Shocked' by Medical Diagnosis She Thought She Wasn't 'Old Enough' to Have

Jennie Garth is opening up about her life with arthritis. The Beverly Hills, 90210 alum, 50, opened up to PEOPLE Thursday about the "shocking" moment she received an osteoarthritis diagnosis – a diagnosis she thought she was too young to have until she began feeling pain in her day-to-day life.

"I'm just used to being a go-getter and taking care of business all the time. And I had three little girls to raise and I've always had dogs. I've always been up and down on my knees, up and just doing everything, in and out of the car a million times a day it feels like. And those little things started to not feel as painless as they always had," the actress shared. "And so it was just this sort of creeping realization that something was different. That's what sort of caused me to go in to the doctor initially."

Garth was then diagnosed with osteoarthritis around age 45. "I was sort of shocked to hear that news from my doctor after going in and complaining about some pain in my knees and my hips and different places around my body and wondered what was going on. And I was shocked to hear the word arthritis come out of his mouth," she recalled. "Because I kind of associate arthritis with... I'm not old enough to have arthritis. Let's put it that way. But yeah, you can have arthritis at any age and I wasn't really aware of that."

Having been so active throughout her life, Garth says she wonders if years of physical activity played a role in her diagnosis, but the star revealed she also has arthritis that runs in her family. "I started talking to my mom and other members of my family, finding out that they suffer from it as well. So many people do but they don't want to talk about it," she shared. "So it was one of those situations and just sort of acknowledging it and being open and honest about it. Let's talk about how to work with it, how to fix it, how to alleviate some of the pain."

Garth celebrated her 50th birthday in April and said she's "definitely" in a good place managing her health. "It's something that you just start to sort of live with and learn how to manage and through different products and different exercise and diet regimes. It's not like it's debilitating in any way. It's just something that you're aware of," she shared with the outlet. "And as we get older, it's really very important... It's very important to be your own health advocate. You're sort of the CEO of you. You really run your business. Because no one else is going to."