Paul Godfrey Fenech met the child at a barbecue in 1980, abusing his trust by later inviting him and his friends back to his home to ride horses when the sexual offending took place.
As the 66-year-old was sentenced on Friday, the Penrith District Court heard he was confronted by the victim, two of his friends and family and beaten up in his home soon after the molestation.
"They gave him a hiding. They knocked him into the pantry and he fell to the ground. They dived on him and kept punching him," Judge Michael Allen said.
Soon after it occurred, the victim's mother called police to report the sexual assault of her son.
"'Police just said to go and sort it out yourselves and if we get a call we'll be slow to respond," the mum allegedly said.
No formal statement was taken and officers only arrested Fenech in February 2022.
Judge Allen said a substantial reason for the four-decade delay was a failure by police to act promptly on the information disclosed to them, instead acting in "too leisurely a fashion".
"The cause and the duration of the delay require that a degree of leniency should be extended to the offender," he said.
The 66-year-old watched Friday's sentencing by video link from Long Bay jail.
"I just want to go home," Fenech told his solicitor Adam Ly before the sentence was handed down.
Judge Allen imposed a maximum jail term of four years with a non-parole period of two years.
The sentence were backdated to July 21, 2022 given the abuser's time in custody and onerous bail conditions after his arrest, meaning he will be eligible for parole on July 20 next year.
Fenech pleaded guilty in March to indecent assault of a male, buggery and detaining for advantage after a plea deal was struck with prosecutors.
On the night of the offending, the boy woke up on Fenech's bed.
"He was naked. He felt like he was unable to move or speak. The offender was next to him. He was also naked," agreed facts seen by AAP say.
Fenech then sexually abused the boy, who was 10 years younger than him and who at one point asked for a drink of water in an attempt to flee.
He was forced back into the bedroom, where his sexual assault continued and he was threatened if he told anyone.
Judge Allen said crimes of sexual assault against children should be viewed with abhorrence.
He acknowledged the serious impact of Fenech's target, who told the court at an earlier sentencing hearing that he had been the victim of sexual assault for 40 years.
"This statement demonstrated to me and I anticipate the community and the offender, the human impact of crime and a life tragically altered by that crime," the judge said.
The court found that Fenech had achieved rehabilitation in the community, being seen as a reliable, kind neighbour and assisting in community activities such as beautifying nearby nature strips and taking three months to help deck the street out with Christmas lights.
Previously jailed to life imprisonment for murder in July 1987, Fenech was released on parole in April 2006.
He had been rehabilitated into the community by committing no offences in the 16-year period from then until his 2022 arrest, Judge Allen said.
