The judge told Cooke, 72, that he would not be considered for release until he had served at least five years and then only if the Parole Board was satisfied he was not a danger to the public.
Mr Justice Poole, sitting at Wolverhampton Crown Court, told Cooke that pre-sentence reports were unanimous that, despite his age, the convicted child killer remained a serious danger to children and young adolescents.
A hearing at Manchester Crown Court in October had been told that Cooke attacked the boys on several occasions during the 1970s when he was travelling around the country doing casual fairground work.
The horrific assaults came to light after a television appeal following his release from prison last year. He had served nine years for the 1984 killing of Jason Swift, 14, during a homosexual orgy.
Cooke, of no fixed address, admitted five counts of indecent assault and five counts of buggery committed between 1972 and 1978 at the October hearing. He pleaded not guilty to eight other counts - which were ordered to lie on the file - and showed no emotion as he was led from the dock to begin his sentence.
Mr Justice Poole said the case was aggravated by the fact that the two brothers had been "groomed" by Cooke.
In each case, Cooke had groomed the youngsters to such an extent that they regarded the abuse as normal.
"The reports before me are unanimous that, not withstanding your advancing years, you remain for the time being and will remain for an incalculable period, a serious danger to children." The judge added that Cooke suffered from a peculiarly dangerous sexual fixation upon children, bracketing him with sex offenders of the "highest level of risk".
The Manchester hearing was told that the boys, from a disadvantaged background, were just 13 when the assaults by Cooke began.
Sir John Nutting QC, for the prosecution, told the court: "Cooke systematically embarked on a course of sexual abuse, so frequent and so manipulative that the boys came to regard a sexual relationship as the natural relationship between adult and child."Reuse content