Upset about the noise they were making outside his apartment at around 4.30am, the senior citizen yelled out from his window to tell them to quieten down, according to a cantonal police report.
The group, who had just left a nearby club called Le Petit Palace, ignored his request and one of them threw a stone at the window.
Following an angry exchange of words, the man responded by using a handgun to fire in the air and then at the partygoers, amid the cobbled streets of the historic quarter.
In the process, a 28-year-old man was wounded in the stomach, police said.
The man, identified as a prison guard, was taken to the emergency ward of the cantonal hospital.
His life is not believed to be in danger.
Police arriving on the scene established a security perimeter around the apartment building where the elderly man lived.
After police negotiated with the senior, he gave himself up without resistance.
An investigation into the case continues.