The International Gymnastics Federation said in a statement that it "does not consider the explanations and evidence provided to date in regards to these athletes as satisfactory."
Dong got a Beijing Olympics credential with documents that suggest she was only 14 in 2000, said Andre Gueisbuhler, secretary general of the FIG. Her blog also indicates she was underage in Sydney, when China won the bronze medal in the team competition.
Yang, who also won a bronze medal on the uneven bars in 2000, said in a June 2007 interview that aired on state broadcaster China Central Television that she was 14 in Sydney. Gymnasts must turn 16 during the Olympic year to compete.
"I would hope that the whole world in sport realizes that the FIG is serious about these rules and the ethics and moral questions," Gueisbuhler said.
Calls to Yang and Dong's mobile phones rang unanswered Wednesday, a national holiday, as did phone calls to the Chinese gymnastics team's media officers.
"We are satisfied with the information provided by FIG, and we now consider the (2008) matter closed," said Emmanuelle Moreau, spokeswoman for the International Olympic Committee.
"Clearly they feel that there is more to be looked at for Sydney," Moreau added. "We encourage them to pursue their inquiry and shed some light on these cases. We now rely on them to get to the bottom of that and get back to us."
Doubts about the ages of China's current gymnasts swirled for months before the Beijing Olympics, with media reports and online records suggesting some girls could be as young as 14. Three days before the games ended, the IOC asked the FIG to look into the matter one last time.
The investigation was expanded after questions were raised about the 2000 team.
"We did not have another choice," Gueisbuhler said last week. "If we want to remain credible, then we have to look into things."
Underage gymnasts have been a problem since the 1980s, when the minimum age was raised from 14 to 15 to protect young athletes from serious injuries. The minimum age was raised to its current 16 in 1997.
North Korea was barred from the 1993 world championships after FIG officials discovered Kim Gwang Suk, the 1991 gold medalist on uneven bars, was listed as 15 for three years in a row. Romania admitted in 2002 that several gymnasts' ages had been falsified, including Olympic medalists Gina Gogean and Alexandra Marinescu.
"We applaud the serious efforts of the International Gymnastics Federation and International Olympic Committee to conduct an investigation given the level of speculation that existed," said Steve Penny, president of USA Gymnastics. "We believe the continuing investigation regarding the evidence from the Olympic Games in Sydney underscores the importance of maintaining a fair field of play and identifying methods to prevent questions of this nature in the future."
While it continues to investigate the ages of Dong and Yang, the FIG also is exploring its legal options and what sanctions might be available. The FIG's statute of limitations in disciplinary matters is five years, and 10 years for criminal cases, and the international federation is trying to determine whether Australia or Switzerland would have jurisdiction. If cause is found, the punishment could be as severe as stripping the medals.
"In our statutes, our code of discipline, we have a range of sanctions. It can be from a suspension, it can be taking medals away, it can be taking the rankings away," Gueisbuhler said. "Are we entitled to take action for medals or rankings at the Olympic Games? Or does this fall strictly under the IOC authority? We are looking at this moment at these questions."
But the medals aren't really the issue, said Dominique Dawes, a member of the U.S. team that finished fourth in Sydney.
"The important issue is them righting a wrong and hopefully prohibiting future Olympians from being underage," Dawes said. "It's really about making sure every athlete is doing things the right way."
Gueisbuhler said the documents Dong used for her Beijing credential list her birthdate as Jan. 23, 1986, which would have made her 14 - and too young - for the Sydney Games. Dong was a national technical official in Beijing, working as the secretary on vault. She was not part of any judging panel.
"If that document is the correct one, that would suggest she was 14 years old at the Sydney Olympic Games," Gueisbuhler said.
Dong's birthdate in the FIG database is listed as Jan. 20, 1983.
Dong's blog also says she was born in the Year of the Ox in the Chinese zodiac, which dated from Feb. 20, 1985, to Feb. 8, 1986. Dong has not denied that, but she refused to answer any questions about her age, telling the AP last week, "I've left the gymnastics team."
"If the FIG wants to investigate this matter," she added, "I will provide every form of documentation."
The FIG also has a copy of Yang's 2007 interview, in which she seems to contradict her official birthdate. Yang's birthdate is listed as Dec. 2, 1984.
"At the time I was only 14," she said in the CCTV interview, done in Chinese. "I thought that if I failed this time, I'll do it again next time. There's still hope."
But Yang, who is engaged to Beijing men's all-around champion Yang Wei, told the AP last week that she had misspoken, declining further comment.
"Everyone has misspoken before. On television shows, there are always slips of the tongue," she said, declining to comment further.
The FIG's announcement that it was closing the investigation on the 2008 team was hardly a surprise. China had insisted - heatedly and repeatedly - that all the girls were old enough to compete, and that it had the documents to prove it.
China provided the original passports, ID cards and family registers for He Kexin, Yang Yilin, Jiang Yuyuan, Deng Linlin and Li Shanshan, all showing the girls were 16 or would turn 16 this year.
"For the FIG, the age of the Chinese team is well documented and proven," Gueisbuhler said.
In August, the AP found registration lists previously posted on the Web site of the General Administration of Sport of China that showed He and Yang were too young to compete. And a Nov. 3 story by the Chinese government's news agency, Xinhua, suggested He was only 14.
"My family and I are pleased with the level of scrutiny the FIG and IOC undertook with this very serious issue," said Olympic all-around champion Nastia Liukin, who finished second to He on uneven bars on a tiebreak.
"When the questions arose originally in the press, all anyone in the gymnastics and Olympic communities wanted was closure, which we now have."
Younger gymnasts are considered to have an advantage because they are more flexible and are likely to have an easier time doing the tough skills the sport requires. They also aren't as likely to have a history of injuries or fear of failure.
China blamed the discrepancies on Web sites and paperwork errors.
"Be it with the age, be it with doping, be it with judges," Gueisbuhler said, "if we believe in fair play in sport and to be a role model for youth and we believe in the values of the Olympic movement, then I think it is our duty to be serious about it and do all we can to ensure these rules are enforced."
Associated Press Writers Graham Dunbar in Geneva, Stephen Wilson in London and Anita Chang and Gillian Wong in Beijing contributed to this report.