A kid can be trusted as soon as he has the maturity and coordination to use a soldering iron safely. That could be 5 years old or 50. I built my first Heathkit when I was 9 or 10. A VTVM. I already had a scope. My father wasn't competent with anything mechanical or electrical. I learned it all on my own. I made a lathe with old washing machine parts and brazed stuff by sticking it into the burner on the gas water heater or the furnace. My parents never knew most of the stuff I did. Some was fairly dangerous but I'm not dead yet and I still have all my appendages.
I would have liked one of those glass blowing kits. Maybe they still sell one.
Wow , we have similar stories! My father was the same way.
I had been building plastic model kits from 7 or so, got interested in all kinds of mechanical and electronic devices about the same time. Might have been around 9 when I was allowed to use a solder gun and mess with HV electronics. I'm still here too!
I guess it depends on how the kid handles those dangerous things whether to let them do it unattended.