A judge ordered Martin Olej, 22, should serve at least 12 years in prison before he becomes eligible to seek release.
Olej, who has autism, was found guilty of the murder of John McCulloch at his home in Port Glasgow, Inverclyde, in August 2009 by setting fire to the house while the victim was inside and unable to help himself.
At the High Court in Edinburgh, the Lord Justice Clerk, Lord Carloway, said that as far as he could see it was unprovoked and followed "the generous decision" of the retired welder to allow Olej and a former co-accused in for a drink.
Lord Carloway said only one penalty could be imposed, which was life imprisonment.
The judge said that in setting the minimum term he took into account he came from "a caring and supportive family" and had psychological difficulties, including the diagnosis of autism.
Olej, of Bearsden, East Dunbartonshire, and Iain Starrett, 21, of Port Glasgow, were charged with the murder, which they denied. Starrett was acquitted on a not proven verdict.
The pair, who were teenagers at the time, had gone to the home of 69-year-old retired welder Mr However, when the victim was lying on the floor unconscious or unable to seek help, Olej poured lighter fuel on to a carpet and chair and set it alight.
Defence counsel Donald Findlay, QC, said Olej was "clearly a man with difficulties" who had "a number of problems".