There's a 15-year gap between Gagai, 35, and the 20-year-old McLean, who will mark up on the 338-game veteran in Sunday's preliminary final at Accor Stadium.
Time waits for no man, but in Newcastle's unlikely finals campaign, Gagai is doing a fair job of turning back the clock.
Over the past two weeks, Gagai has survived battles with two of the NRL's most damaging centres - South Sydney's Latrell Mitchell and Leka Halisima of the Warriors - to help put Newcastle into the last four for the first time since 2013.
There were many detractors of Brisbane's decision to sign Gagai for 2027 but his finals form and big-match experience have earned him plenty of admiration.
Not least from McLean, who was just four when Gagai made his NRL debut in 2011.
"He's probably playing some of the best footy he has ever played," said McLean.
"He's been around for so long but he doesn't let that get to him, he's such a competitor."
McLean crossed paths with Gagai two years ago when the Penrith centre's older brother Jesse was part of a Maori All Stars camp alongside the Newcastle centre.
It was Gagai's ability to get past Halasima and unleash a one-handed offload that set up Dominic Young for Newcastle's winning try against the Warriors last week.
McLean knows how that feels. Last year in a round 12 loss in Bathurst that sent Penrith to the bottom of the ladder, McLean missed six tackles as the Knights tore the Panthers to shreds.
"Being able to play against him, I've won a few and lost a few and he knows how to get the best out of himself and (I have to) understand and respect him for the amazing player he is."
McLean has come out of the other side of that humiliation to establish himself as one of the NRL's most potent young centres in his short, 49-game career.
He won State of Origin selection for NSW earlier this season and is expected to feature for New Zealand at this year's World Cup.
"I'm in my 16th year of the NRL and he's only just starting so for what he's been able to achieve, it's nothing short of amazing," said Gagai.
"But in saying that, I understand what he's capable of and what he brings to that Panthers team. He's a big body, athletic, tough. He's got a strong ball carry.
"I've got to make sure I'm doing my job and hopefully I can go out and execute."
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