Darragh Lyons, with an address in Chapelizod, Co Dublin, admitted causing Alanna Quinn Idris serious harm during an assault in Ballyfermot on December 30, 2021.
Lyons also pleaded guilty to the assault of teenager Louis O'Sullivan during the same incident.
Quinn Idris lost the use of her right eye after being hit with the saddle of an e-scooter and knocked unconscious during the attack, while O'Sullivan was stabbed and violently beaten.
Lyons admitted to punching Quinn Idris in the face before jumping over her and attacking O'Sullivan.
Handing down the sentence on Thursday, March 23, Judge Martin Nolan said the attack was "premeditated" and "savage", adding that Quinn Idris was trying to protect her friend, who was the target of the attack.
Judge Nolan said he did not believe that Lyons wanted the victims to suffer serious injuries but said he was involved and culpable by common design, according to the Irish Independent.
He also took Lyons' age into account, stating that young people do "irrational and stupid" things. He also stated that Lyons had no previous convictions and had cooperated with the investigation.
Judge Nolan said the maximum sentence for assault causing harm was life in prison, adding that the state had recommended a sentence of 10 to 14 years.
Two other men are currently before the courts in relation to the attack, while another individual, who is believed to have hit Quinn Idris with the saddle, has never been identified.
In a victim impact statement in court, Quinn Idris described the attack as "vicious and unnecessary," adding that it had destroyed her confidence and her chance of having a normal life.
"The life I was supposed to live was taken away from me before I turned 18," she said.
She said she now has to live the rest of her life disabled, adding that the woman she was supposed to become "died that night."
"Sometimes I wish I never woke up from when I was hit with that object."
Judge Nolan praised Quinn Idris for her "very, very moving" statement.