It was the late Sir Matt Busby, the former Manchester United manager, who first coined the phrase.
A picture of his now immortal quote still hangs in the Old Trafford dressing room today: “If you’re good enough, then you’re old enough.”
The Scot built an all-conquering young side that was tragically decimated in an aeroplane crash in Munich in 1958 before starting almost from scratch to lift the European Cup a decade later.
Two days after the 2005 RTÉ Raidió na Gaeltachta Donegal SFC final, Jim McGuinness gathered the Naomh Conaill panel together underneath the stand at Davy Brennan Memorial Park in Glenties.
In front of a huge support at MacCumhaill Park - the majority in the blue and white of the 6/1 outsiders - there had been a stormy finish to the meeting with St Eunan’s.
The match ended in a 1-5 to 0-8 draw. Naomh Conaill, in their first final since 1965 having never won the Dr Maguire, had surrendered a 1-3 to 0-1 half-time lead.
Their chances required a Brendan McDyer kiss of life, as he pointed three minutes into second half injury time to level the scores.
St Eunan’s raged with referee Mick McGrath for blowing the full-time whistle as substitute John Haran was about to pull the trigger for an attempt at what would’ve been the winning point.
When the dust settled, the perception was that it was St Eunan’s title to lose in the replay seven days later.
John Gildea, at 34, was the hub of that Naomh Conaill side, playing an intelligent game to provide experience in a panel of youth, one that even included a raw 16-year-old by the name of Leo McLoone. From the 15 starters, there were 12 players under 21; three of which were minors.
“We were weary and went to training on the Tuesday night,” Gildea said recently.
“Everyone thought that we had blown our chance but Jim, who had come in that year to help coach us alongside Hughie Molloy, called us in.
“He spoke about how it was St Eunan’s - and not us - that were lucky to get the replay. Everyone took what he said on board. It was, I suppose, reverse psychology.
“He really made us change our perception of the replay. Everything was turned into a positive. He gave the young lads incredible belief.”
Naomh Conaill, still believing, used the same tactics in the replay they had first day out with Gildea running the show from the base of midfield.
They flooded the defence, continually frustrating a St Eunan’s side that ran up blind alleyways and when the chance arose, Naomh Conaill broke with conviction.
That was one of McGuinness’s first cuts at coaching - certainly at senior level - and although his approach wasn’t widely appreciated, Naomh Conaill’s 0-10 to 1-5 replay victory remains the biggest shock a final of the Donegal SFC has seen.
Perhaps the most intriguing thing about Naomh Conaill’s triumph was that it showed for the first time locally that a system could overcome spontaneity.
Nicky Brennan, then the GAA President, attended the first match and remarked that there were “children playing for the blue team.”
McGuinness had put his faith in what were essentially children.
With a certain group of the contemporaries having pushed over the 30-mark in the Donegal panel McGuinness has managed for four years, there was a requirement to infuse the set-up from the bottom-up.
Ten minutes before referee Joe McQuillan was due to throw the ball in for Donegal’s Ulster Championship opener against Derry in May, a hush fell on Celtic Park when the stadium announcer informed the 15,000 or so in attendance of the two late changes to the Donegal team.
Already without the suspended Rory Kavanagh, McGuinness opted to leave his two other protagonists at centre-field - Neil Gallagher and Martin McElhinney - on the substitutes’ bench.
Paddy McGrath made a first appearance in nine months and Leaving Cert student Darach O’Connor’s participation raised some eyebrows.
The slightly-framed, nippy corner-forward, nicknamed ‘Jigger’, blasted over his side’s first point of the day. Donegal went onto win 1-11 to 0-11.
“I did have a laugh when I saw Paddy McGrath and Jigger in the middle of the park on The Sunday Game graphic - that has to be the smallest midfield ever named!” McGuinness joked afterwards.
“Jigger’s first point, you could see the pure pace,” Eamon McGee added.
“It was actually scary looking at him. I mark Colm McFadden and I mark Michael Murphy in training, but I don’t go anywhere near Jigger. There’s just no point!”
Under McGuinness, Patrick McBrearty famously played both minor and senior grades one afternoon against Antrim in 2011 and has featured in every one of McGuinness’s 20 championship matches to date. McBrearty has yet to turn 21.
Ryan McHugh, McBrearty’s Kilcar clubmate, is now so well embedded it’s sometimes forgotten that he’s also just turned 20.
Odhran MacNiallais enjoyed a fine start to life with the senior panel in the Allianz League Division Two this term and McGuinness had little hesitation plumping for the 21-year-old to slot in at centre-field at Celtic Park.
“He has put the hours in practicing,” McGee added of his clubmate. “You could see from a young age that Odhran was going to be special.
“Everybody in Gweedore knew that. It was a case of marrying the ability with the attitude that’s required for an inter-county player. He’s done it and made the step up.”
Four weeks after overcoming Derry, when Donegal were facing Antrim in the Ulster semi-final, there was another couple of late alterations.
O’Connor and MacNiallais were brought in for Karl Lacey and Kavanagh, who were suffering respective hamstring and abductor muscle injuries.
Donegal won 3-16 to 0-12 with O’Connor scoring 1-2, whilst MacNiallis registered 0-4 from play and won the man of the match award.
“They’re carefree in a way,” McGuinness added of his youngsters.
“They really want it and are pushing it to not only be in the team but to be team players. They’ve added a nice new and a fresh dimension.
“We wanted to give them a good go at it in the McKenna Cup and the League. They’re comfortable on the ball and that’s what I like.”
O’Connor’s goal, on 48 minutes against Antrim, proved his traits of speed, fearlessness and confidence in a microcosm.
Having picked up possession from Murphy in midfield after Donegal had swarmed out Antrim’s Patrick McBride, O’Connor made a beeline for the Antrim goal playing a give and go with Frank McGlynn.
“When I got the ball in the middle of the field the only thing on my mind was goal,” O’Connor admitted afterwards.
With Kevin O’Boyle, the Antrim corner-back turned sweeper closing in, O’Connor swayed right.
Showing maturity away beyond his 18 years on only his second championship start, O’Connor lashed the ball into Patrick Flood’s bottom left-hand corner. It was a splendidly taken goal.
“He’s a special player,” McGee added of O’Connor, having recalled first witnessing him in the 2013 Ulster U-21 semi-final when Donegal pipped Derry 2-11 to 0-15.
“We were up to watch an U-21 game one night - myself, Michael and Neil Gallagher - up in Healy Park. Michael earmarked him and said: ‘This is the player we need’.”
“You are always analysing where you are at as a team, saying that you could do with this type of player or that type of player,” Murphy said.
“Darach was always one, so was Patrick, and Ryan as well and you are thinking they will fit in and there are more like Luke Keaney, Marty O’Reilly.”
As Sir Matt Busby said, they’ve proven they’re good enough, so they’re old enough.
“The young lads have given it an infusion as well, an infusion of fresh legs and fresh mindset,” McGuinness added.
“They’re hungry for game-time and hungry for their own scores and to be a part of something.”
McGuinness, when he was just 19, was part of something when he was the youngest member of the 1992 Ulster and All-Ireland winning panel.
Now, the new generation want to follow those footprints.