Wales coach Warren Gatland's matchday squad on Saturday could comprise a third or more of players aged 23 and under.
And fly-half Jones, the most capped player in Welsh rugby history with 102 Test match appearances, believes their impact cannot be understated.
Players like skipper Sam Warburton, his back-row colleagues Dan Lydiate and Tony Faletau, wing George North, centre Scott Williams and wing Leigh Halfpenny have all made significant contributions towards a World Cup campaign that could be Wales' best since 1987.
"Team morale is fantastic," Jones said.
"The younger players have a high rugby ability, and they've gone out there and enjoyed throwing the ball around. They have been top-drawer.
"They are fearless. They back themselves, and the fact so many good youngsters have come through, put their hand up and raised the bar has really had a good knock-on effect throughout the whole squad.
"It is certainly the most competitive squad I have been a part of. It is a nice situation for the coaches to be in.
"It is great for us that everyone is challenging and everyone is knocking on the door. You have got to enjoy these challenges as players."
No-one has made a bigger impression during Wales' World Cup journey than 6ft 4in teenager North, who made every New Zealand newspaper's team of the pool stage.
He has amassed nine tries in 12 Tests - three during the World Cup - and could perhaps produce the spark that might take Wales into a semi-final against England or France.
"George is a great person, such a likeable guy," added his Scarlets colleague Jones.
"He is a good professional who works very hard on his game. He is ambitious, and I can't speak highly enough of the guy.
"He is top-drawer. He deserves all the credit he gets as far as I am concerned.
"Both teams are going into this game on the back of good performances, and I am sure the mood is high in both camps. It's a big situation.
"It is special, simple as that, because of the excitement, the occasion and what it means. It is the quarter-final of the World Cup.
"We play against their players in our domestic campaign, and internationally quite a bit too, and we know them well, but this is going to be a special game - a one-off, winner takes all.
"A mixture in our performance is key. What we can't become is predictable in our attack. We have to have variety, and I am confident the game plan we have gives us that.
"What is important is we implement that and try to manipulate defences so we can play a great style of rugby.
"We need to go out and express ourselves. There is good belief. We need to be brave and play with a lot of excitement.
"It is purely concentrating on ourselves, getting our own house in order and ensuring we are as prepared as we can be. We need to make sure we deliver a performance."
Assistant coach Neil Jenkins, meanwhile, has welcomed the return of Wales' World Cup injury casualties ahead of tackling Ireland.
Full-back James Hook, wing Shane Williams and flanker Lydiate all trained with the squad at Wellington's Newtown Park today.
And it means Gatland is set to have a full complement of 30 players from which he can choose his starting line-up.
All three players have been sidelined since the punishing Pool D victory over Samoa in Hamilton 17 days ago that put Wales firmly on course to qualify for the knockout phase with world champions South Africa.
Hook suffered a shoulder injury and went off at half-time, Lydiate lasted just 10 minutes before ankle ligament damage sidelined him, while Williams missed appointments with Namibia and Fiji because of a thigh strain.
"You always want your best players fit," Jenkins said. "These guys coming back in gives the squad a huge boost - a huge lift - and there is fantastic competition for places in the squad.
"With Ireland, we play them year in and year out and we know it is going to be a very tough game. They are a very tough side, a very physical side.
"If you win on Saturday, you are in with a shot (of winning the tournament).
"Over the last couple of years the games have been pretty nip and tuck between us. Since 'Gats' came in, we've managed to win two and they've won two."
The heavy rain of the past two days in Wellington relented as the Wales players headed to training, and although further downpours are forecast, Saturday's prediction is for dry conditions.
"It is a matter of getting the balance right as to when to keep the ball in hand and kicking it at the right times," Jenkins added.
"The weather, I am sure, will play a part, but we will just have to adapt to that. I'm sure these games will be a little bit tighter than they have been in the group stages."
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