Northampton Saint North will be 23 years and 138 days when he runs out at the Aviva Stadium in Dublin.
He has scored 22 tries and played three Lions Tests, but Gatland wants more from his giant wing.
"I think he's got the ability to be a lot better than he is," he said.
"He's had 50 caps which is fantastic but I think there's still a lot of improvement.
"And probably in the last 12 months he hasn't played as well as we would have liked, he's aware of that and we've been working hard on his game."
North will be playing for the first time in five months following an enforced lay-off to recover from concussion.
He scored a hat-trick of tries on his last appearance for Wales against Italy in the 2015 Six Nations, and scored two for the British and Irish Lions during the 2013 Test series against Australia.
However, Gatland believes North's recent international form has not been up to the standards he believes the player is capable of because of a tendency to become peripheral to the action.
"Players of that ability need to get their hands on the ball," he added.
"He probably went through a couple of campaigns where his touches weren't enough, and he made some defensive errors so it was pleasing to see some of that confidence has come back into his game [against Italy]."
However, Gatland, who first capped North as an 18-year-old against South Africa in 2010, said North's achievements were "fantastic".
"What he has achieved in the game at such a young age is exceptional," he said.
"I remember seeing him as an 18-year-old playing for the Scarlets and saying 'look we have to cap him as soon as possible because there's a freakish talent there'.
"I don't think we've seen the full extent of the potential he still has to be and a player and we still haven't ruled in the future that he couldn't be an outstanding centre as well."
George North becomes the youngest player to win 50 caps for Wales when they play Ireland on Saturday, with coach Warren Gatland insisting there is still room for improvement.