"I think she's an amazing woman and an amazing competitor," Campbell said. "I really admire her. I'm not going to be swimming when I'm 40. No way."
Torres is looking to pad her stash of Olympic medals.
She earned her 10th career medal last weekend, anchoring the U.S. women to a silver in the 400 free relay. But she wants an individual souvenir from her fifth Olympics, a record for an American swimmer.
Torres was the bronze medalist in the 50 at the 2000 Sydney Games. She retired but launched her comeback after giving birth to her first child in 2006.
"I've been working on my starts," she said. "My finish was horrible, but hopefully by Sunday I won't think about anything, I'll just do it."
Torres is in Beijing without her personal coach, Michael Lohberg, who found out last month that he has a rare blood cancer.
Marleen Veldhuis of the Netherlands was second overall in 24.38. Libby Trickett, the world record-holder who earned a silver in the 100 free earlier Friday, was fourth in 24.67. She is the only woman to have gone under 24 seconds, clocking 23.97 at the Australian trials in March.
"It's going to be a fast final so I've really got to bring it each round," she said. "It's obviously a very different format to have the finals in the morning and the heats at night. I really want to make it through to the next round, but once you're there, it's anyone's game."
Trickett first recorded a sub-24-second time in a race against Michael Phelps in April 2007, but swimming's world governing body refused to ratify a world mark because it was a mixed gender race.
Also advancing among the top 16 were 100 champion Britta Steffen of Germany (sixth); Therese Alshammar of Sweden (ninth); and American Kara Lynn Joyce (14th).
Joyce, who was fifth four years ago in Athens, added the sprint event to her schedule after Jessica Hardy withdrew from the team because of a positive drug test at the U.S. trials.
The women sprinters and distance men took over the Olympic pool on a night when Phelps rested after claiming his sixth gold medal earlier Friday, with a world record in the 200 individual medley.
He will try to tie Mark Spitz's record of seven golds in Saturday morning's 100 butterfly final against teammate and world record-holder Ian Crocker.
"People point at me," Crocker said, acknowledging his status as the potential villain in Phelps' quest. "But (Milorad) Cavic is looking real good and lots of other guys are looking really good. It's going to be a tight race across the board."
With Phelps catching precious sleep at the athletes' village, his teammates were busy trying to secure him a spot in lane 4 for the 400 medley relay final -- Sunday's closing event of the nine-day swimming competition. By then, Phelps could be poised to win his eighth gold.
Matt Grevers, Mark Gangloff, Crocker and Garrett Weber-Gale succeeded, finishing first overall in 3 minutes, 32.75 seconds.
They were careful not to false start or fail to surface beyond 15 meters -- both of which could have meant the end of Phelps' historic run.
"This relay might be what it all comes down to for eight golds," Grevers said. "You don't want to be the one who screws that up. I don't think we were going to leave China if anyone DQ'd us."
Crocker did just that at last year's world championships, getting disqualified for taking off too soon in the prelims, which spoiled Phelps' chance at eight golds. It was on Crocker's mind this time.
"It's something kind of hard to forget, which I guess is a good thing at the same time," he said. "I don't want to do something stupid. I want him to have every shot that he's got."
Those four are likely to be swapped out for the final, with Aaron Peirsol, Brendan Hansen, Phelps and Jason Lezak taking over and trying to win gold for the seventh consecutive Olympics.
Australia qualified second in 3:32.76, followed by Japan in 3:32.81.
The American women have been nearly as dominant in the medley relay, winning it eight of 12 times. But their last victory was in 2000, when Torres swam the butterfly leg.
Margaret Hoelzer, Megan Jendrick, Elaine Breeden and Joyce qualified third in 3:59.15 for Sunday's final. They trailed Australia (3:57.94) and Britain (3:59.14).
Grant Hackett of Australia retook the Olympic record in the 1,500 free prelims, qualifying fastest in 14:38.92 for Sunday's final.
He's trying to become first three-time winner of the 30-lap race. Hackett denied countryman Kieren Perkins a three-peat in 2000, when Hackett won for the first time and Perkins took the silver.
"I had a cold for a couple days and I didn't tell anyone. I don't know how it got out," Hackett said. "But it's no big deal. I had to go out there swim a good pace, placed a good time and it's just a matter of getting ready for the final."
Ryan Cochrane of Canada erased Hackett's Olympic record from Athens two heats earlier, finishing second overall in 14:40.84. Yuri Prilukov of Russia was third and Zhang Lin of China fourth.
David Davies of Britain, the bronze medalist in Athens, moved on in fifth. American Larsen Jensen, who lost to Hackett in 2004, grabbed the eighth and last spot in 14:52.11. His teammate Peter Vanderkaay didn't advance, finishing 11th.