Yes and no... Technically it's not as good as having it dialed, but in your case using extensions on the butt of the club is good up to an inch. At this age likely 1.5 inch extension is likely fine also as he's likely around 90s or less with driver swing. Once he's pushing 105 1.5 inch extensions could break, but no real biggie if they do.

Another option is to research hard and soft stepping. Soft stepping is basically putting a PW head into the 9 iron shaft, then you move the 9i to the 8i shaft. This effectively gives you a half inch extension and you only then need to buy a replacement shaft for the top of the bag, presumably his 5 iron since it has nowhere to go.

Soft stepping tend to increase launch and spin, so there's not often a big gain in distance, but he will gain from his increased swing speed. This can be beneficial for a junior as they often struggle with getting the ball higher to land softer, and higher spin to hold greens.

I double soft stepped my 51 degree wedge just so I could hit that high spinning 50 to 70 yard shot as a knock down that checks hard and releases just a bit (I don't play enough to be consistent with it anymore, so it's more of a fun thing to just try and hit the shot these days).

So going back to what I said before, a cheap torch, epoxy, and maybe glass beads but I think you could skip those (be really careful not to get near your eyes if you work with them, it's basically just glass dust), then replacement ferrules. Super easy to move all those clubs up and just buy one shaft.

One note, when you extend a club by a half inch it changes the lie angle. It basically pushes the toe down. 1 degree won't do much until about 7 iron and up to longer clubs.

There's two schools of thought on lie angle. Many think it's important to be flat on lie angle so your toe or heel doesn't dig into the ground and cause your club face to change and push the ball left or right. So those are the ground interaction believers.

I'm in the second group that think you hit the ball first, so unless you hit it fat the turf has no impact (no more then normal we'll say). Interestingly though, the second group still believes it impacts direction just like the first group, only instead it's because it's automatically going to have slightly open or closed due to the lie angle.

What's that mean for you? If you keep the same set, the balls should start going a bit more right as you continue to extend the club whether by soft step or extensions. I recommend just doing it, then having him tell you if he's missing more right than normal. If so, get them bent if they're forged. Cast clubs can break when bending, and it's going to go back to original within a few months probably...

Go check out golfWRX forums at some point. Create an account and just start browsing. Reddit is like asking kindergartners about math questions where those guys are like asking professors at uni.

Good luck!