The 28-year-old Rousey appeared on the "Joe Rogan Experience" podcast Monday, discussing the future of her already distinguished career.
"I don't want to be fighting in my 30s," Rousey said. "By 30s, I mean 31, 32.
"If you're actually 30 years old, that's not 30s -- that's 30. Once you add into 31, that's 30s, plural."
The Los Angeles-based Rousey's focus is gradually shifting toward the film industry. She has appeared in several major Hollywood movies and is scheduled to begin filming a Peter Berg-directed action film "Mile 22" in January. She also is planning to portray herself in a film produced by Paramount Pictures.
But a fight between Rousey, the UFC bantamweight champion, and Justino has loomed over female MMA for years. The UFC and Rousey (12-0) have stated that Justino (14-1), who holds a featherweight title outside of the promotion, must drop to Rousey's weight class.
Many believe Rousey's career would be left unfinished if that fight never materializes. A former U.S. Olympic bronze medalist in judo, Rousey seems to at least partially agree with that take.
"It seems unfinished -- my career," she said. "There's more left to do. I don't feel like I'm done yet. With the Olympics, you win an Olympic gold medal and you're done. With the UFC, when am I done?"
When asked specifically by Rogan, a UFC commentator, if a fight against Justino would help Rousey feel as though her career was over, Rousey answered, "that definitely would."
"If she never steps up, I'll know," Rousey said. "I'll probably go on a little longer waiting for her [to drop in weight], see if she shows up sooner rather than later. I don't know how much longer I'd go."
Justino has expressed doubt she can make the 135-pound weight limit, although earlier this year, she and her management guaranteed Justino would make the weight if the UFC booked a fight against Rousey in December. The UFC went another route and eventually scheduled Rousey to make her seventh title defense against Holly Holm at UFC 193 on Nov. 14 in Melbourne, Australia.
Rousey has long stated her belief that Justino could make the weight if she's not using performance-enhancing drugs. Justino served a one-year suspension in 2011, after she tested positive for anabolic steroids in California.
Since then, Justino has passed multiple random drug tests in Nevada and California -- but Rousey remains unconvinced Justino has discontinued her use of PEDs, based mostly on her physical appearance.
"You see what happens when people get off steroids -- you see what they look like," Rousey said. "It's very easy for them to drop down. They immediately shrink up. It changes everything. It's all an insecurity thing.
"When you look at these people from when they were using and after, they look entirely different. Cyborg looks and weighs exactly the same. If she gets off, it will be very easy for her to make the weight."