IDK for sure but it was just before joining Boy Scouts so I was about 9-10. I remember getting my Boy Scout knife that looked like a Vic sak Pioneer but had a black textured handle and silver bolsters.
I got it as a Christmas present from my dad when I was 7 or 8. It was a 3 blade folding Remington.
Over 20 years later and it's still in great condition. I still use it regularly.
I expect I was around 7 or 8 with my first Barlow knife. The first knife I bought for myself was in 1981 at the New Mexico State Fair. It is an Uncle Henry and I still carry it.