Police also confiscated a cake the protesters wanted to distribute to the public to celebrate what they said was Museveni’s 73rd birthday.
The veteran Ugandan leader claims he does not know his exact date of birth but says he was born in 1947.
However, the opposition claims that he is 73 years old and that he is deliberately lying about his age to circumvent the country’s laws imposing an age limit of 75 on any presidential candidates.
Museveni easily won re-election in February.
“The aim of the demonstration was to call attention to the lies over the president’s age so that at the next election he cannot stand,” opposition activist Muhammed Ssebirinya told AFP.
Ssebirinya said they had worked out Museveni’s age by researching his school records and talking to former classmates.
“From all this we worked out that he is around 73 years of age,” he said.
Police said the they stopped the protest for security reasons.
“We could not allow such an event to take place for the safety of people’s businesses in the area,” Vincent Ssekate, police deputy spokesman, said.
Opposition protests over rising living costs in April led to a brutal clampdown by security forces that left at least 10 people dead across the country.