By Mark Trevelyan

RIO DE JANEIRO (Reuters) - Not content with seventh place at her seventh Olympics, Uzbek gymnast Oksana Chusovitina declared on Sunday she would be back to compete in Tokyo in 2020 at the age of 45.

Minutes after taking part in the vault against gymnasts younger than her 17-year-old son Alisher, Chusovitina breezily announced she would keep going.

"Of course I'm not entirely happy with today's performance, but what are you going to do? So we are going to move forward," she said.

Over the course of an extraordinary career, the diminutive Chusovitina has competed for the Soviet Union, Germany - where she lived for a period while Alisher was receiving successful treatment for leukemia - and Uzbekistan.

Her first Olympic appearance was at Barcelona in 1992 where she won a team gold with the Unified Team of athletes from the former USSR.

She flirted with the idea of retiring after each of the last two Games, but there was no hesitation when she was asked if she would be back in Tokyo for Olympics number eight.

"Definitely," she replied. "I've already taken this decision... I just woke up in the morning and decided.

"I'd like carry out an experiment to see how long it will take before I've had enough."

Her gymnastics lifespan almost defies belief, as the next oldest competitor in Rio after her is 32-year-old Vasiliki Millousi from Greece.

BILES TRIBUTE

Vault winner Simone Biles of the United States paid tribute to her. "She's amazing. If there's one person that could do it, it is only her," said the American.

Warmly greeted by the Rio crowd, Chusovitina began each of her two attempts by raising her right hand, then standing erect with her right foot outstretched to prepare her sprint for the springboard.

On the first, she over-rotated her vault and crouched down on the landing before rolling over. On the second, she had to step slightly to the side to maintain her balance at the end.

After the competition, in a special tribute that she described as a pleasant surprise, spectators were shown a short video of highlights from her long career.

She bowed, waved and blew kisses to the crowd in what many must have assumed was her final Olympic appearance.

Not so, said Chusovitina.

And what does her son think of her decision to carry on?

"He doesn't know yet," she said.

(Reporting by Mark Trevelyan; editing by Ken Ferris)