The fact that it took him 15 years to understand what was happening is not unusual.
"Some people are like, 'oh, no, I'm trapped in the wrong body', and have known that since they were a toddler," he says. "But some people are like me and don't know it that early. There a lot of people who are older than I am before they realise."
Worried about the reaction, he never outed himself at school but says Napier Girls' was already making an effort to be inclusive before he left.
"Instead of saying 'good morning, girls', it would be 'good morning, everyone' or 'good morning, students'," he says. "They're doing a good job."
Jay is thankful for the support his family has given him as he transitions, but says he's never taken grief from anyone over his decision.
"New Zealand is generally a pretty chill place. People are becoming more aware of all of this stuff. There's less fear about it, and more understanding."
Besides, he says, "it's my business what's in my pants. The most important thing for me is that I'm a man".
Breast removal is a future goal, but Jay says he doesn't mind his body.
"It's served me well so far," he says. "There's some parts of it that I like less than others but I'm not one of those people who go, 'oh, god, I hate my body'. I'm more, 'how can I alter this to benefit me'."
As for what the advice he'd give someone who is unsure about their situation, he says it's important to "build up a support group and do what you have to to stay safe".
"If they're in the closet, if they can't be who they feel they are, because they think society at large is going to be against them, I'd say society is a lot better than you'd expect it to be. You'll be able to get out of the closet at some point to be who you are."