Alan Mills, now 54, molested the first victim in Dawley, and the second in Teignmouth both about 20 years ago, the court heard.
A judge at Exeter Crown Court praised the first victim's courage after she read out an impact statement in which she said the abuse had condemned her to a life sentence of mental torment. She finally called an NSPCC helpline in 2017.
It was only after learning that Mills was being prosecuted for the first offence that the second victim came forward.
Mills, of Upper Hermosa Road, Teignmouth, denied indecent assault on the first girl and indecent assault and indecency with the second.
He was found guilty at the end of a four-day trial and jailed by Recorder Miss Kate Brunner, QC this week.
She put him on the Sex Offenders Register and made a 10-year sexual harm prevention order which will prevent unsupervised contact with female children after his released.
She told him: "The first was absolutely terrified by your assault and said it felt like it lasted for an eternity. I have heard her victim personal statement read with great dignity.
“She described what you did to her as a life sentence."
Mills said both girls had invented the allegations and that he could not even remember meeting the second one.
Heather Hope, defending, said the two offences were isolated incidents in an otherwise hard working and praiseworthy life.