The current European Junior BMX champion is one of the leading lights in British cycling at the moment, and at just 18 has his whole future ahead of him.
But things could have been so different for the Preston-born star, after a day that would have convinced many people to never want to take a seat in the saddle.
“When I was six, my dad had a really bad accident on the road cycling into work,” said Cullen, speaking at a SportsAid event dedicated to championing the parents and guardians of talented young athletes.
“He ended up in a bad way – he broke his neck, cracked his skull, fractured his eye socket and he couldn’t work for the best part of a year.
“One day up to the hospital we spotted a little BMX track. It’s such a weird thing that cycling had put my dad’s life on hold for six months and that’s what got me into the sport I’m in today.
“We went down with a cheap old mountain bike I had when I was younger and I just bonded with it instantly.
“My dad’s the person that I thank for getting me here, although maybe not in the conventional way. It’s inspiring that cycling put him in that position, but he was still there to get me into it and helping me into the new light where my career is now.”
After that unusual introduction, Cullen has gone from strength to strength on the BMX circuit, claiming two World Junior BMX Championships, as well as competing at the 2018 Youth Olympic Games in Buenos Aires.
But just like his dad 12 years ago, Cullen has experienced his fair share of scrapes in a sport that is constantly teetering on the edge, with every slight deviation having the possibility of disaster.
The start of last year is the perfect example of that, with three crashes in quick succession for the young star, which prompted his decision to take some time away from the sport.
“I was going into the season the best I’d ever felt,” Cullen said. “Physically and mentally I was confident, but in the first race of the year I managed to crash on the first lap of practice which was a freak accident.
“Then when I was recovering back home I had another crash in training.
“Following that I crashed a third time in Norway, so after that I took a break from racing for two months.
“I just focused on myself and at that point it was more for my mental wellbeing – getting back my confidence was quite hard after taking some heavy hits.
“It worked really well, the week after getting back on it I won the National Championship in Glasgow, then the week after that won the European gold in Latvia, so it did the job.”
This year sees him make the step up to the elite Championship Level, and while primitive thoughts of this summer’s scheduled Tokyo Olympic Games are never far away, it is a trip to France in 2024 that the youngster already has in the diary.
He said: “Tokyo is a potential but it depends on how everyone rides this year, so it could be on the cards but most likely 2024 in Paris will be my time to shine.
“It’s a sport that is so random, there are so many factors, so many variables that can change on the day, even due to weather.
“You’ve got to be fully switched on, you can’t be half asleep if you want to be a BMX rider, not a chance.”
SportsAid supports the most promising young British athletes by providing them with a financial award, recognition and personal development opportunities during the critical early stages of their careers. Please visit www.sportsaid.org.uk to find out how you can help the charity support the country’s next generation of sporting heroes.