Rubick showed the boys pornography, engaged in masturbation and oral sex and some of the acts were filmed.
Police found 12,157 objectionable images in his possession.
Rubick admitted the charges.
To support his appeal, Rubick supplied a statement of contrition, a statement of personal change, a statement of his own history of sexual abuse as a child, and a report from prison psychologist John Watson about his treatment.
The information outlined strategies Rubick had implemented in prison to change thought processes and avoid high-risk situations after release.
The Crown opposed the admission on the grounds the information was not "fresh, credible or cogent".
Rubick's lawyers also argued that the judge erred in not finding his age a protective factor. They said there was insufficient evidence to show that a lengthy, definitive sentence would not provide enough protection for the community, given the intensive treatment programmes available in prison, Rubick's motivation to attend such programmes and his addressing of his own childhood experiences.
The possibility of an extended supervision order was put forward.
In rejecting the age argument, the Justices said there were similar cases where preventive detention had been imposed at such an age as Rubick's.
They said a decline in health, or successful treatment would play a bigger role in reducing the risk of offending than age.
Julian Hannam and Megan Boyd acted for the appellant, J E L Carruthers for the Crown.
The appeal was heard by Justices Kos, Fogarty and Mallon.
