Raymond Harrison, 69, abused the girls when they were aged under 13 between 1979 and 1982, Carlisle Crown Court heard.
He denied 12 charges, including four rapes, but was found guilty by a jury.
The woman raped by Harrison said he was a “pathetic sick creature” who had “robbed me of my childhood”.
She told police he threatened her at the time and told her “nobody was to know because it had to be our secret”, the court heard.
Prosecutor Kim Whittlestone told jurors Harrison, who lives off Penrith Road in Keswick, groomed the girls.
She said: “They liked him. They trusted him. He would buy them sweets and the odd cheeky cigarette.
“The prosecution case is quite simple: that he did this so he could, when he was alone with them, sexually touch them and they wouldn’t complain.”
The charges included six counts of indecent assault, four counts of rape and two counts of indecency with a child.
The woman raped by Harrison said: “He has robbed me of my childhood and ruined my adult life in so many ways.
“He has made me feel guilty for his actions while he continued to live his twisted and privileged double life. I am serving a continuous life sentence.”
The second woman recounted a “harrowing” trial, adding: “Being the victim of childhood abuse creates an injury that can’t be mended or forgotten about. In addition it creates an unaccountable guilt and feeling of deep shame.”
Harrison, who was in his late 20s and early 30s when the offending occurred, insisted during his trial there was “absolutely nothing at all” in the girls’ claims.
He maintains his denials and an appeal is pending, the court heard.
Recorder Ciaran Rankin told him: “It is quite clear on the evidence you groomed each of these girls independently and went on to sexually assault them in the way the jury determined that you did.”
Harrison must sign the sex offenders register for life and follow the terms of a sexual harm prevention order.