Full-back Halfpenny, 22, will be among eight players aged 23 or under in Wales' matchday group for the Eden Park showdown.
And such a statistic is testament to Gatland's belief in young players, many of whom have taken this World Cup by storm.
"Warren spots talent, and once he sees that he believes in the player and brings him in," Halfpenny said.
"It has brought a new dimension to the team, and it is paying off.
"We have just gone about our business quietly and have always believed we could be serious contenders. We have strength in depth.
"I hope we are inspiring young kids. Young players have come into the side and played how they know they can. They have brought a freshness and given a real buzz to the atmosphere.
"I went from the (Wales) under-20s to the Lions in one year. At the start of that season I was hoping to play for Cardiff RFC and maybe get a couple of chances for the (Cardiff) Blues. Suddenly, I was playing for Wales."
Wales are braced for the biggest game in their history tomorrow, with victory meaning a World Cup final place against New Zealand or Australia back at Eden Park on Sunday week.
And a key off-the-field performer during Wales' campaign has been squad psychologist Andrew McCann, whose work with the players has proved critical in build-ups to such big games.
"I have worked closely with him, and there are different approaches," Halfpenny added.
"There may be a switch-off session early in the week which can be helpful, and then when the game beckons I go through my roles and get them clear in my head.
"If I am nervous, it relaxes me. It is about being composed, and then we know we have to focus for the week after.
"We enjoy the victory and then get back to work the next day.
"I wanted to be a professional rugby player from a young age and I had to make sacrifices on the way, such as not going out with my mates.
"I was focused in what I wanted - and I am not looking back with regrets.
"My grandfather Malcolm was a big role model. He used to play for Swansea and took me kicking every week, keeping me motivated.
"(Former All Blacks star) Christian Cullen was a player I admired. I loved watching him, and it's mad to say because I am in the same team now, but Shane Williams was a player I looked up to and wanted to be like."
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