My first pocketknife was an old, rusty, used-up camping/scout-style knife I had appropriated from my dad’s toolbox at age 13. Not long after, I bought some Schrade pocketknives for myself (not all at once) at a local hardware store. Which was lucky; at some stores you had to be 18 or older to buy a pocketknife. This was in early 1977.
As for how old someone should be, it totally depends on the person. Some kids are taught well and are mature enough to safely and responsibly handle a pocketknife at a very young age. There are many adults I wouldn’t trust with a pocketknife and should never carry one. I was taught to respect knives as a toddler, to the point that my parents knew the kitchen knives were safe around me, and I wouldn’t touch one without supervision, much less play with one, because at that age I was frankly afraid to.
I would not try to be “smart” and bring a knife into a location, like an amusement park, a courthouse, a concert or sporting event, etc. Or a school. Although when I worked as a real-time captioner for hearing-impaired students at local colleges and universities, I carried an SAK in case my steno machine needed adjusting, etc. I wouldn’t try it as a student.
When I was a kid, most of the boys at school, and many of the male teachers, carried some type of pocketknife, and nobody I knew of ever pulled one out during a fight. They weren’t viewed as weapons. Nobody cared in the ‘70s/early ‘80s. Nowadays, forget it. You’ll probably end up on the news if you’re caught carrying a Boy Scout-style knife or a Victorinox Classic at school.
Jim