The offensive behaviour charge relates to an incident in May in the Bayfair Shopping Centre carpark where Nelson approached a man and made sexual propositions to him.
The propositions were shunned by the victim who alerted store security and police were called.
Police prosecutor Sergeant Sean Brennan sought a jail sentence of between two to two-and-half years before any discount was allowed for a guilty plea.
Nelson's lawyer Bill Nabney argued for a lower starting point, citing the 28-year gap in offending.
Mr Nabney said despite all the times Nelson had been to prison before, he had never received any treatment for his sexual offending, and hopefully that would happen this time.
Judge Callander said, depending upon which prison Nelson went to, there were some excellent treatment programmes for longer stay prisoners.
Nelson, who had been assessed as being at high risk of further offending, had significant psychological issues in terms of his attitudes and behaviours, the judge said.
Judge Callander said because of Nelson's "lifetime of paedophilic interests", it was vital he take advantage of the treatment programmes offered to him while in prison.
"They don't profess to cure people but they do help offenders to manage the issues, so if you are attracted to commit perverted behaviours with young children, hopefully you will not act out your perverse instincts," the judge said.
Outside court, the victim's father told the Bay of Plenty Times that he was "gutted" that Nelson did not receive a longer sentence given his past convictions.
"It took a lot of courage for me to get up in court ... but my son means everything to me. You can be sure I'll be there when the time comes for him to come before the Parole Board asking to be released from prison,' the victim's father said.
