I for one am a big proponent of the classic scout knife as a first knife for a kid. In fact, I do a GAW every year to give scout knives to kids. I've already done this year's GAW (you can find it here
https://www.bladeforums.com/threads/scout-knife-memorial-gaw-2022.1830512/), but I encourage you to enter this next January when I do the next one. Unfortunately, these days, it is hard to find a BSA branded classic scout pattern knife, but I will probably be buying some of the Deluxe Scout pattern knives, as well as a Cub Scout pattern (and
@willintheweeds has been donating made in the USA Bear and Son Cub Scout knives to my GAW for years now!). I am currently a little low on scout knives, I was hoping to be able to scour the OKCA show for good condition scouts this year, but once again the pandemic put off the show. Hopefully in 2023 we can get back to having the show here in my hometown.
There are certainly arguments to be made for a variety of different knives. I like the use of slipjoints for first knives because a) if the kid can't get them open safely, they are too young for the knife, and b) the lack of a lock teaches good safety habits (though those lessons can certainly come with a little blood). The scout knife is just a good all around knife that can be useful at all ages. I keep one in my backpack all the time (in fact I just changed my backpack knife from an old USA made Camillus to a Sheffield made scout knife given to me by
@Johnnythefox).
As far as the right age, I think that depends on the kid. I felt fine letting my oldest daughter use a knife under close supervision at 3.5, my son is currently 5.5 and I still don't let him use a knife even under supervision. My oldest daughter is 8 now, and has her own small knife collection, and I don't worry about it. At the rate my son is going, I think he might be a legal adult before I am fine letting him have his own knives. We'll see how I feel about my youngest daughter having knives when she gets a little bit older. They are all very different people.