Their louder than a magnum pistol, whether that will bother a kid who is just learning to shoot is anyone's guess.
I think it's safe to say it won't improve his training.
............Here in certain shooting circles that I`m very familiar with, everyone seems to shoot them pretty darn good.
And believe it or not, and given the same cartridge and charge levels, the noise levels between the 20" tubes vs the 16.5" ers, are not all that much different. And certainly with good hearing protection on (which should be worn anyway regardless of barel length???), the noise levels to the ears are at best minimal between these two barrel lengths.
So by most accounts, anyone contemplating owning a shorter barreled compact rifle, should not get one with a barrel length less than 20". The fact is, that the noise levels from a barrel 3.5" shorter such as a 16.5", has a minimal increase where noise and blast is concerned.
On several occasions when I fired a friend`s 23" 375 Ruger African right along side my own 20" 375 Ruger Alaskan using the same identical factory ammo, there was no discernable difference in blast or noise levels between them. Same holds true between a 16.5" tubed 300 RCM ruger compact vs the 20" version in the Ruger Hawkeye.
Imo, most complaints about noise and blast levels from the shorter barrels, usually come from those who didn`t wear any hearing protection? Yes, the shorter tubes are louder. But they are not all that overwhelming as long as good hearing protection is worn. Without protection, hearing can still be adversely affected with 24" and 26" tubes too.
But as always, tolerance levels do vary from person to person. Within my circle of friends anyway, I guess that we are just a little more noise and muzzle blast resistent.
My late dad started me bench shooting a 30-06 at 9 years old. Mastered it within a few weeks before I was 10 and took me on my first hunt before I was 11. That`s probably one of the reasons why extra blast and noise levels have no affect and are of no consequence to me.
For some kids, a shorty 243, 260, 7/08 would work, while for others, they would not.