Summer signing Archie Gray, from Leeds, has made 40 appearances this term.
Postecoglou, ahead of Sunday's trip to Liverpool, said: "With all of these things, people just look at them as a moment of time. If you had have said at the start of the year that Lucas Bergvall, Archie Gray and Mikey Moore would have played the amount of time they have as teenagers, I wouldn't have said that that's impossible.
"They've played a lot, they've played a lot because they've earned it, obviously opportunity as well, but Archie will play, he'll play even between now and the end of the year, he'll play significant minutes.
"Just the games haven't worked out the way we wanted them to, and we needed to get game time with other guys.
"He's fit, he's available, other guys, it wasn't the case. As I said, we've got a real clear focus about where we need to be for the rest of this year and who needs to be in a good physical condition. Archie is in good physical condition, others weren't, so we had to give them some game time but there's no doubt that Archie will play a significant role still for the rest of this year."