Ian Knowles, 20, from Waterloo Road, was jailed for 19 years over the killing of Robert Morrison, 69, who lived in Grove Road, Kings Heath.
Knowles carried out the cowardly attack alongside Asmaila Mohamed, 20, of Geraldine Road, Birmingham - who was jailed for 17 years.
The duo broke into Mr Morrison's home on December 10, 2018, where they beat Mr Morrison in order to steal his bank cards, mobile phone and jewellery. Knowles was armed with a knife, although he used the weapon to carry out threats, while Mohamed was masked.
They had waited for Mr Morrison to leave his favourite pub and arrive home in his mobility scooter on the night, before smashing their way into his home at 9.40am.
The frail victim was left with three rib fractures and was so frightened by the ordeal he did not tell neighbours about what happened until the following day.
Knowles had robbed Mr Morrison on three occasions previously where in one incident, he was forced to hide in a cupboard.
Following his latest robbery ordeal, Mr Morrison was taken to hospital and was discharged three days later.
But he was taken back there after a concerned neighbour called police, where officers then found him in immense pain. Sadly, he died just three days after that.
Both defendants were handed further 13 year jail terms for the robbery of Mr Morrison, which judge Melbourne Inman QC ordered to run concurrently at Birmingham Crown Court.
Knowles was also jailed for 12 months over the possession of a bladed article and 14 days for possession of cannabis, which he will also serve concurrently.
Both men, who were 18 at the time, were convicted of murder by jurors following a trial. Mohamed was also convicted of robbery while Knowles pleaded guilty to that charge at a later stage.
Knowles carried out the attack on his 18th birthday. The defendants had met one another while living at a hostel.
Sentencing Knowles at Birmingham Crown Court, Mr Inman said: "Mr Morrison was a small, frail man with ill health and wasn't mobile.
"Despite that, he enjoyed life and frequented the same public house where he enjoyed being in the company of peers.
"You saw him as a vulnerable victim and robbed him on a number of occasions. Mr Morrison was clearly frightened of you.
"He was so frightened of what happened he didn't tell his neighbours until the following morning.
"It is clear you intended to cause him really serious injury in order to gain access to money. Sadly, the rib fractures affected Mr Morrison's ability to breathe.
"He died several days later."
The court heard Knowles had written a letter to the victim's family and the judge expressing his remorse.
Balbir Singh, the defence counsel for Knowles, said: "In this case, death was neither foreseen or contemplated by either defendant. There was no intention to kill.
"This case was about robbery with a little degree of planning which was not very great. That was the focus of what they were about that evening. They were not planning to cause serious harm. The infliction of serious injury was likely to have happened on the spur of the moment."
The court heard that Knowles had a long standing mental illness and he had not been taking medication for that during the time of the attack.
George Carter-Stephenson, defending Mohamed, said he had left his father's home which he "bitterly regretted" as it led him down a "wrong and criminal path".
"It led him to associate with Mr Knowles and he accepts if it wasn't for that, he wouldn't find himself in this position today."