Andrew Hendry attacked the elderly man while he was walking in Stirling Road, Tullibody in the early hours of Saturday, 13 March.
The pensioner needed hospital treatment and Hendry was arrested near to where the assault happened.
Hendry pled guilty to one charge of assault to danger of life at Falkirk Sheriff Court last month.
His prison sentence of two years and four months was confirmed today, Tuesday, 18 May.
Detective Constable Debbie Reid from the Criminal Investigation Department based in Stirling, said: “This was a despicable act of violence and was a completely random attack.
“At the time Hendry was under the influence of drink and drugs with his actions leaving lasting scars for the victim and his family.
“I hope that the sentence today will offer them some closure and I would like to thank the victim, along with witnesses to the incident, who assisted with our investigation.
“We will continue to tackle violent crime within our communities and ensure offenders are held to account for their crimes.”