The teenager fled downstairs and told his uncle, who also worked there.
Steele also twice took a 17-year-old boy who he knew through the church band to a South Perth apartment that he kept secret from his wife and kissed him, telling him he was "special".
"In essence, it appears you were leading a double life," Judge Ronald Birmingham said during sentencing on Friday.
Judge Birmingham said Steele last offended when he was aged 46 and while he'd got on with his life, his victims had carried the burden of what happened to them.
One of his victims, a relative, had been shunned by family members who didn't believe him but said in his victim impact statement he felt a great weight lift from his shoulders after he testified at Steele's jury trial in April.
Judge Birmingham said the offending was persistent and he could not suspend Steele's jail term as the punishment needed to reflect the community's condemnation of such crimes against children.
As he was led out of the dock, walking slowly with the help of a cane, Steele's wife of 52 years tried to hug him but was prevented by security.
He will be eligible for parole when he has served half of his term.
- AAP