Before that, he had one conviction of possession of cannabis plants.
A report in relation to the assault said given it was his second conviction, risk of reoffending was low.
The report noted Kay-Selwyn was bullied in school and dropped out not long after joining the Killer Beez gang at the age of 14.
Kay-Selwyn told a probation officer he regretted his wasted years and wished he could go back to primary school and make changes.
RNZ