She said there was no real evidence of remorse and that Moses had a number of previous convictions. He was subjected to prison release conditions at the time of the aggravated robbery.
Moses' lawyer Kelly Ellis said by putting his hand up and pleading guilty at the earliest opportunity, he could not have been more cooperative with police.
On Moses' denial that he didn't possess a knife during the robbery, Ms Ellis said her client didn't dispute the summary of facts and the surveillance footage.
He hoped to get out of jail, secure a job and to live a productive life, she said.
Judge Murray Hunt said being the eldest of the four who decided to carry out the robbery, Moses should have exercised restraint or prevented the crime. His victims, he said, felt fearful, lacked confidence and had concerns about their wellbeing since the robbery.
One Gull staff member who was assaulted had to go to the hospital and the service station manager had to employ extra security, Judge Hunt said.
Moses was supported in court by his mother.
At 20, the judge said Moses had racked up a significant number of previous convictions that included theft and multiple convictions of burglary. Judge Hunt said Moses had a number of opportunities in the past few years to change his behaviour but failed to grasp them.