"It's really disappointing because I'm a long distance runner," says the youngster who is only permitted to compete with the Open men on turning 14 this year.
Harrison, who has cerebral palsy, carries a classification of a T35 physical disability (the smaller the numeral the higher the degree of disability).
Para athletes can be physically or visually impaired, therefore, someone who is in a wheelchair, for argument's sake, can be last over the line and still be declared a winner based on world classification times.
Tomorrow Harrison will compete at the Hawke's Bay/Gisborne Championship before finding his mark alongside Open men in his maiden New Zealand Championship meeting in Dunedin early next month.
"It's my first time. I'm very excited to see who else will be there."
The prospect of lining alongside older Para athletes inspires him and he welcomes stiffer challenges.
Says mother Vickie: "Para athletes' parents will hold a meeting in Dunedin to see if we can push for long-distance events."
Asked what are his chances of making an appearance in Tokyo, Harrison replies: "It could happen."
It frustrates him that there's a widespread perception that the sprint races are ideal for para athletes.
"I don't have a chance in 400 metres. At the 400-metre mark my legs just start getting into the race," says the teenager whose T35 1500m record is 5m 52.46s although he feels he needs to be quicker over the distance to compete seriously.
He suspects other people in New Zealand who have the stamina to do longer distances like him are probably a little apathetic because there's no beaten track for 800m and 1500m races to the Paralympics.
"If they hear about me running they may also want to do it."
Harrison is under no illusions about how much harder he'll have to work with Cull if he's to realise his international dreams.
"All the workouts with Mick and the rest of the training group has helped me a lot."
The impending Dunedin parents' meeting will endeavour to take a small step in trying to secure a pathway for the events to be staged in Australia to give the para athletes a taste of international meetings.
Harrison's father, Keith, a maths teacher at NBHS, believes relay teams may also help break down barriers for Para athletes.
Cull, who started preparing Harrison 28 months ago, is impressed with his incremental progress that led to another record time.
"It's just another example of this boy's determination and courage. He is destined to set more distance records over the next few years," he says.
"He has all-round skills and over the recent holiday period shot a 74 round of golf in North Auckland.
"He is so lucky to have supportive parents who ensure he has a well-balanced life."
Harrison last year, through Hawke's Bay Today, enlightened fans who often wondered how he found himself on a podium after a race when he finished last among a bunch of able-bodied runners.
His presence has caused a division among followers, even in the HBPB arena, of those who are comfortable and those who still can't comprehend why he's in the line up despite the meeting announcers notifying everyone of his disability.
The former Tamatea Intermediate pupil was diagnosed with cerebral palsy at the age of 3 following a "feveral convulsion" which resulted in him losing balance and mobility, as well as speech and cheat death a few times.
Intense therapy followed as the youngster showed tremendous determination and courage to go on to accomplish feats such as playing golf, train five times a week with Cull and speaking.
The outlook was bleak at 3 with experts predicting Harrison was never going to ride a bike, swim or write, albeit more slowly than others.
Consequently the Harrisons are indebted to paediatrician Kate Robertshawe, physiotherapist Karen Busch, podiatrist Alarna Tuck and swim instructor Lisa Rennie for helping their son.
