I talk about this myself. It’s not that skills can’t be taught at any age. But in general it’s easier at a certain age.
In my opinion, this has nothing to do with fear. People talk about an age that fear sets in but in my experience that is incredibly individual. Younger kids often have more fear than older kids, you can outgrow fear as well as grow into it.
I find (in girls) tumbling skills and bigger skills are easier to learn prior to puberty. If I can get a gymnast to a certain level before puberty, we tend to be able to continue to progress really well in the teen years. If not their progress slows.
Meanwhile things like dance skills and finesse are usually easier to teach after puberty.
There are several reasons why it’s easier to teach big skills before puberty.
1. Growth. Prior to puberty growth is generally slow and steady, during the puberty years it’s often sudden. Kids have to constantly get used to a new body. Injuries are also more common as body parts grow at different rates.
2. Strength to body weight ratio. Younger girls have a lower centre of gravity and as they are smaller they need less strength to make the skills happen.
3. They are easier to spot and catch.
4. They have more energy. When you set up drills your younger kids wills usually bounce around taking a tonne of turns. Older kids tend to be slower about it. When the little ones fall they often bounce up a thousand times abs have another go, teens are not usually like that.
5. Pressure. Teens have a lot going on peer pressure, pressure to look cool, school pressure, social pressure, stress. Their brains are so busy processing so many things. Young kids can often live more in the moment and just focus on the skills at hand.
6. Brain flexibility. Kids have a huge number of neural pathways in their brain. Each one they tap into with switch on. In the teen years unused pathways are shedded. This means it can be easier for a child to learn something new but a teens brain works more efficiently as it has less neaural pathways but new skills can be harder.
7. Younger kids can be less self conscious. Teens go through a stage of being very easily embarrassed. Kids tend to be less afraid of trying something new, falling on their face, messing up etc.
There are more reasons, this is just a start. It’s a generalisation. It’s not the same for all kids and is generally not the same for boys at all.