There's an old saying that sometimes it's not the size of the dog in the fight, but the size of the fight in the dog that really counts.

Brisbane-born teenager Tom Gilbert may not have heard Mark Twain's quote before but it is something that sums him up well as he embarks on his path to playing NRL for the Queensland Cowboys.

At just 80kg, Gilbert concedes considerable size to his rivals, who, like him, are still growing.

I'm happy not to be the biggest guy on the field.

Tonight, in the Under 18s interstate curtain-raiser to the State of Origin clash at Melbourne's iconic MCG, Gilbert will have to chop down players more than 20kg heavier.

He loves the challenge but the Cowboys are keen for him to pack on more weight next season in his bid to play NRL.

That's not an invitation for him to pig out on Maccas, KFC and pizza, but it's a loud and clear message the club and coach Paul Green want him to fill out his frame more in readiness for the next step of his budding career.

"They want me to be 94 or 95 kilos next season," he told QRL Media.

"I'm not worried about, it's just gaining weight.

"They're happy with how I am now, I am coming back from a shoulder reconstruction last August.

"They've been focusing on getting my shoulder right and getting me back to fitness.

"I'm happy not to be the biggest guy on the field."

Thurston inspires

Watching Cowboys star Johnathan Thurston, who is not overly big, take on the line and take the hits is inspiring to Gilbert.

"He (JT) is only about 80kg. When he gets hit, he is up for the next play. He just worries about doing stuff for his teammates and getting the job done," Gilbert said.

"Even when he cops a late hit, he still gets up and doesn't complain, he just keeps playing.

"I remember a semi-final against Brisbane when he got whacked by Josh McGuire.

"He hurt his ribs and he looked like he was going to throw up but he just got up and kicked a drop goal.

"He didn't do it for himself, he did it for his team."

Controlled aggression

Gilbert's laid-back temperament is well suited to the slower chilled-out lifestyle of Townsville.

But he is anything but slow, calm and relaxed on the football field.

"I use my aggression on the field to motivate me and fire me up but I know I have to control it," he said.

"You want to keep your discipline under control and manage your aggression and use it to your advantage."

Find something extra

Gilbert has previously pulled on the maroon jumper in the Under 16s in 2016 and again for the Under 18s last year.

"When you play a club game you are chilled and relaxed but when you step up to these rep games there's much more intrigue and you have butterflies in your stomach all day before the game," he said.

"It's exciting, you embrace it more every time you pull on the maroon jumper and represent the people of Queensland.

"You have to find something extra inside you because the game is just so much quicker."

Cowboys dream

Gilbert said he'd had the opportunity to do a couple of opposed sessions with the Cowboys NRL squad which had opened his eyes.

"Just to be around Johnathan Thurston and Matt Scott, those guys, it puts things into reality to how they train and prepare.

"I'm hoping to make it with the Cowboys and right now is about getting myself physically prepared to push for a spot.

"I've got all the right people up there to help me make it."

Gilbert's first memories of Origin still makes him laugh.

"My whole family were mad Queensland fans when I was growing up. I still remember my first game watching Darren Lockyer run out in those old Queensland jerseys when I was about six.

"I was excited all day.

I fell asleep just when they kicked off because I was so tired and pumped all day

"It was a free dress day at school, so I wore my Queensland gear.

"I came home all excited and mum had cooked a good feed.

"The whole family sat around the TV to watch the big game but I fell asleep just when they kicked off because I was so tired and pumped all day."

Igniting the fire

Gilbert's first live experience of Origin - the 100th game at Suncorp Stadium in 2014 – went much better and left a significant impact on him.

"I remember the pre-game atmosphere and the game, it ignited a bit of a fire in me to be the best player I could possibly be," said Gilbert.

"I wasn't necessarily thinking I would play Origin but it made we want to be the best player I could be and be happy with that.

"When I come off the field and I feel disappointed, I know it's because I didn't give 100 per cent.

"I don't like that feeling.

"I don't even like it at training because you know mentally that you've catted it, not just to yourself but to your family, they're the ones who believe in you and have invested the time and money in you so you feel you have cheated them if you don't give it 100 per cent."

Fight in the dog

If you are looking for Gilbert in Wednesday night's game, look for one of smallest kids who keeps knocking bigger guys down and who keeps getting up and giving it his all.