Tim Duncan was a kid the last time he met the Thunder in the postseason. He was only 38 years old then.

Duncan played 39 minutes in Game 6. He finished with 19 points and 16 rebounds. And his final shot bounced on the rim, with 19 seconds left in overtime, before falling.

“I got the roll,” Duncan said with the impatience of youth, “finally.”

Duncan was still a kid last spring, too. In Game 7 against the Clippers he played more minutes and scored more points than any Spur. And after his free throws tied the game in the closing seconds, he came within a quarter of an inch of blocking Chris Paul’s winner.

This is the way it’s been these past few years. In the tensest games of the playoffs, when others fade, Duncan seems to get younger.

Now it’s supposed to be different. Duncan is not sure which knee is his good one anymore, and he’s not sure what’s coming from night to night. He tied for 10th on the team in shots attempted against Memphis, and, in one game against the small Grizzlies lineups, he played the fewest minutes of his long postseason career.

But now? Against a big lineup that fits him?

The Thunder will bring out the best in Duncan — and help him determine whether this is his last season.

A coin flip might as well determine a match between two healthy, deep, star-led teams. The Spurs will win, leaning on experience and the home court, but it will take the full seven games.

Oklahoma City’s end-of-game decisions will be tested, as will Billy Donovan’s learning curve. Danny Green will need to make shots, and then there’s the question a longtime NBA official asked this week:

“Is Kawhi Leonard ready to be the go-to guy in the last two minutes of playoff games?”

Somewhere in the middle of this will be someone who has been on the outside as of late. Just a year ago Duncan scored 20 or more points in four of the seven games against the Clippers. This entire season, including the playoffs, Duncan has scored more than 20 points just once.

Those on staff don’t think he’s changed as much as the teammates around him have. In that Game 6 against Oklahoma City in 2014, after all, Matt Bonner started next to him.

With LaMarcus Aldridge and David West, there aren’t as many minutes to go around, and the Oklahoma City series will take that further. Boban Marjanovic will get some change-of-pace minutes against the big Thunder frontline.

Duncan has acknowledged he understands. “I’m here to win,” he said in Memphis. “Whatever it takes, it takes.”

His actions say as much. And last winter, when he missed a string of games because of a sore knee, he went to the practice facility as he has for his career, alone and determined, putting up shot after shot.

One Spurs official observed that at the time and was hopeful about this summer. Doesn’t Duncan love the game too much to retire while he can still play?

Duncan still can play. Even in the Memphis series, when he averaged 20 minutes a game, he averaged two blocks a game. Some in the media have made public that they voted for him on their all-defensive teams, and then there’s the defensive real plus-minus stat from this past season.

Duncan finished second only to Andrew Bogut — and ahead of Draymond Green and Leonard, among others.

But Duncan has also said he would prefer to be on the floor. And in a league going smaller, led by Golden State, there’s reason to wonder if sitting on the bench bothers him more than he lets on.

Or, as another put it last week: “Tim is superhuman. But he’s also human.”

The Spurs don’t know what Duncan’s plans are. One on staff guessed last week he thinks Duncan will retire this summer.

Here’s another guess: Duncan needs a reason to return. And competing now as he has in the past — whether he’s angling for a Russell Westbrook drive or boxing out Steven Adams — would do wonders.

So would, at age 40, feeling young again.

bharvey@express-news.net

Twitter: @Buck_SA