Eleven years on from when he lined up for Old Scouts in a final at English rugby HQ, the talented wing is a key man for the Saints.
Sleightholme has become a prolific scorer in the black, green and gold, overcoming a series of injuries during the formative stages of his career to show that he is one of the hottest prospects in the Gallagher Premiership.
And now he will look to help Saints topple champions Harlequins at Twickenham on Monday evening.
“Whenever you walk out on to that pitch, it’s a moment you’ll never forget and one you’ll cherish because they are few and far between,” Sleightholme said.
“I played at Twickenham for Scouts when I was 10 in a Gullivers Travel national tournament. We got to the final and we won it.”
Sleightholme will hope for similar success now he has reached the age of 21.
But he knows the size of the challenge that will await Saints.
“Quins have lost a couple of games recently in the Premiership and we’ve lost our last two in Europe so it’s two teams who are coming out to prove a point and get back on the horse,” Sleightholme said.
“The first 20 minutes wasn’t great for us at Ulster last Friday (Saints went 19-6 down before eventually losing 27-22) - we didn’t come out and start how we wanted to.
“But to stay in the fight in a European game like that and to have the chance to win the game at the end shows the character we had to fight in that second half.”
Sleightholme started in Belfast, making his seventh appearance of the season.
He has been irked by injuries during his young career but has developed an impressive resilience to being sidelined.
He said: “It’s definitely been a frustrating season so far because of injuries.
“But it’s great to be back being a rugby player now as opposed to just a gym rat.
“I’ve had quite a lot of time injured in the past couple of years so I’ve become numb to it.
“I try not to let it affect me, I give myself targets and plans because that just keeps you a bit more sane through the whole process, otherwise it starts to get on top of you.
“It’s one of those things that comes with the game and you sort of get used to it.
“A lot of it’s just freak incidents, bits that happen that you can’t control.
“It’s not as frustrating when it’s something you can’t control because if you could control it you’d wonder what you could do differently.
“It’s been tough but when I have had my chances, I’ve really enjoyed it.
“I keep trying to play my game and see what happens.”
Sleightholme is clearly maturing all the time, and the wisdom he is gaining is good news for his younger brother, Frankie.
The two siblings both played last Friday, with Frankie turning out on the wing for Saints Under-18s in their derby-day win against Leicester Tigers.
And it left dad Jon having to try to keep up with both matches at the same time.
“He went to Frankie’s game in Bedford and was listening to the radio to see what was happening in Belfast,” Sleightholme said.
“My brother is young, still maturing, still learning.
“He’s different to me in many ways but I’m looking forward to seeing how he goes.
“I try to give him advice.
“Dad gives him advice as well but the game’s changed since dad played - it’s a very different way of playing now.
“He will actually come to me and ask me stuff and I’m always there to help him but I don’t want to force it on him.”
While Frankie is learning from Ollie, Ollie is learning from Courtnall Skosan.
The South Africa wing scored again against Ulster, taking his Saints tally to nine tries in seven starts.
And Sleightholme said: “He’s world class for a reason and he’s proved it since he’s been here. I can definitely learn from him.
“He’s someone I can learn from, whereas if you look at big T (Taqele Naiyaravoro) - I can’t play the game the same way he does because he runs through people, which I probably can’t.
“But Skos and I are more similar than me and big T so there’s a lot more to learn.”