Thirteen or Fourteen
Older societies that were smaller almost certainly landed on thirteen or fourteen as a common age of majority because of things going badly if they tried X with twelve year olds.
So my understanding is older cultures in simpler times frequently used either thirteen or fourteen as the age of majority. Why not all thirteen?
I don't actually know and I'm just spitballing here, but some thoughts:
1. Nutritional status.
Maybe areas that lacked adequate supplies of certain essential brain nutrients took an extra year to get there.
2. Contextual factors.
Maybe people living in more dangerous settings needed to set a higher bar because a mistake could be deadly.
Or maybe people with a relatively cushy existence could "afford middle class values" and were comfortable saying it can wait another year until he or she is more solidly ready for those responsibilities.
3. Cultural differences.
Some individuals are more or less risk averse. There are variations in risk tolerance between cultures as well.
And that's hard to really try to pin down as to WHY.
I've had people describe me as very risk tolerant and I don't think I am. I'm extremely risk averse and conservative.
But I'm also educated and I have experience with certain things. So what seems to happen is people interpret my behavior through the lens of what scares them or what's typical for a woman or whatever and that's not my house for deciding what's too risky.
An example I read decades ago in my teens is that tightrope walkers are obsessed with safety. Like they check everything twice and do so personally.
"Crocodile Hunter" Steve Irwin was said to be more comfortable around animals than people. People are large, dangerous animals and most people recognize that other people can be dangerous and may avoid certain neighborhoods, but most people don't go "I can't go to the mall or the grocery store! There are PEOPLE there! They could ROB me or KILL me!"
I have a dog phobia, but I am not too concerned about coyotes most of the time. If it's not a large pack, most individual coyotes are fairly small and actively avoid adult humans (though they will attack small children). In contrast, an awful lot of dogs run up to total strangers and demand attention while their owner swears they don't bite and are just friendly, which makes me want to slap them BOTH.
If you know a lot about X, you may be aware it's potentially dangerous but it's less dangerous for someone who knows what they are doing.
The Inuit ("Eskimo") are supposedly a very quiet people, probably because noise can attract dangerous predators. In such a situation, you may need to just let youngsters figure some things out on their own without a lot of verbal instructions.
In contrast, my mother talked non-stop in a very informative way and I realized how valuable that was when my youngest son got chicken pox and his dad had no if he ever had it. In my family, you would have been schooled to within an inch of your life that adult onset chicken pox is much more serious than in children and YOU, buddy boy, NEVER had it.
One of the biggest differences between my middle class life for the first forty years or so and poverty since then is that poor people need to keep their voices down and worry more what people may hear.
In a house in the suburbs, a loud argument in your living room probably won't get the cops called on you. The neighbors may know you are arguing or may not, but you probably don't need to worry about getting loud in a verbal argument that doesn't involve physical violence.
Not so if you live in a cheap apartment or are homeless. People who themselves have similarly loud arguments in the privacy of their middle class suburban house will decide homeless people arguing loudly in public because they have no home are clearly a danger and public nuisance and they may dial 911.
If you have any situational constraints on talking a lot, you may give less verbal instruction to the kids and do a lot more showing them. This may be perfectly effective but slower.