At what age do people generally get a gun? I have friends who's father bought them a gun at 11-12, though personally I think 14-15 might be more appropriate.
My experience in the US, for something that's not a BB gun, I'd say 10 or 11, but that's not a hard and fast limit. It's usually a small caliber (like .22) or something. Hunting used to start at 12 way back, although these days I've heard some places allow hunting as early as 8..? The truth is it depends on the individual, and how well they can be trained. This video gives a pretty good overview of "milestones" someone should reach before owning a gun: https://www.youtube.com/watch?v=5fRJTyU851Y
In the UK you can join the Army Cadet Force (ACF) at 12, or in an area without middle schools (most of the UK) 11 if your secondary school has a CCF (Combined).
Probably the most controlled way young people get their hands on them here, perhaps also the most common (competition/clay/game shooting clubs being the other possibility).
Cadets use a modified (no magazine, one in the chamber) .22 Lee Enfield for short range target shooting on-site (perhaps not all sites have them) and L98 (A1 was magazine fed but manually cocked, the semi-automatic A2 came in about ten years ago while I was going through) rifles of the SA80 family that's standard issue (L85) in the British Army. They also have, but use more rarely, L86 LSWs, and others not issued but may be encountered at 'summer camps' and the like, with training from regulars/TA.
It is a slightly scary thought looking back on it being older now, I'm not sure I'd fancy being an instructor: imagine being a teacher with a 'difficult' child, except you're instructing them in handling a firearm...
I enjoyed it a lot though, and would recommend it for sure.
I've instructed kids roughly this age. My context was the American Boy Scouts (remember when that still existed?), so I'm sure it was similar to your experience in the ACF.
There are a lot of psychological techniques you pick up on before you even get to the instruction. One of them is setting a firm expectation that "you are becoming a man, this is how men behave, men are accountable for their actions." This works well for kids in a situation where they feel that they have some honor/face to maintain.
The only difficult child I had to handle was one in the scouts who was using a pocket knife in a very unsafe way. I tore up his totin' chip [1] in front of the class and the shame from that and the dressing down his scoutmaster gave him at the evening campfire straightened him up quickly. I only bring that up because it illustrates how I used that shame drive as what I view as the most important mechanism to keep everyone safe.
This was easy for me to intuit because my father introduced me to guns at a young age, .22's under his supervision around 4 or 5, a BB gun without direct supervision around the age of 8, then on to pellets and carrying my own large-caliber rifle while deer hunting around age 12. It was impressed on me that I was going to pay like hell in corporal punishment if I hit something I shouldn't have, and I've ever had a mishap with a gun (knock on wood.)
It's interesting that in these contexts where I've felt most safe there's an almost visceral understanding that removal of group standing and potentially violence are waiting on the other end of negligence on your part.
[1] https://en.wikipedia.org/wiki/Totin%27_Chip --usually a minor infraction warrants removal of a corner of the chip. A serious infraction warrants complete destruction of the chip.
I got a shotgun for my 8th birthday, though probably started shooting at age 6. I remember the first gun I shot was an AR-15 M1 (triangular hand guard).
I bought my two kids their own .22 bolt action at 7 and 9. Then my son a .22 AR-15 at 10.