There is no way whatsoever Green should be dropped, give him time for goodness sake. This isn't just a kid batsman who might need to work on his game, this is a kid who is the future of his generation, let him grow into the role. He is performing with the ball and in the field, just let his batting come on, let him learn while the team is settled and good enough to compete with anyone. The likes of Warner, Smith, Starc and Khawaja aren't going to be around that much longer, let him drink in as much as he can from them while he can.
You make a good point regarding the old heads... we're not far off losing Warner and co.. and then a few years after that Smith will be gone.
Of the team right now we've got Cummins (28), Marnus (27) and Head (28) as long term players, with Cummins and Marnus being the long term locks in the team. Excluding guys like Jhye, etc. as they are likely to be mainstays in the future, but haven't locked in a role at this point.
Green is a likely mainstay in the team for a long time... and perhaps he should be afforded the same sort of leniencies that Michael Clarke was back when they identified him as a talent to nurture within the test team setup... that move paid off as he eventually became a top top batsmen and future captain for the team.
I also recall that when Clarke took over it was like an AB scenario where he was clearly our best player and doing a lot of the heavy lifting as new players were brought into the team and the former greats retired or neared retirement.
I'm not saying Green will get to those heights, but he looks a very good player and is as likely as anyone to be a mainstay in the team for a very long time.
Like you say keep him around these guys for as long as possible and give him time to grow into the role, because he is likely to be part of the leadership group moving forward.
We know that he's possibly one of the best batsmen going around in Shield cricket at 22, and at test level his bowling and fielding is right up there. When his batting at test level does eventually catch up he's every chance of being within the top 5/6 batters in the country and has already shown a temperament to go for long long innings.
A guy who's 22 and already one of the best bats in Shield cricket should be afforded some time in the test setup when the rest of the team is already performing quite well. It's a near perfect environment to be blooding a guy that they will hope to lean on for the next decade or so of cricket.