The fact that it is possible for a motivated 25-year-old to be better at learning something than the same person as an unmotivated 10-year-old does not refute the fact that human brain development is such that certain forms of learning are much easier at 10 than at 25.
Neuroplasticity primarily relates to the evolved ability of young children to rapidly, effortlessly acquire basic, evolutionarily critical behaviours - language systems and other core social behaviour necessary for tight social integration (and later various more complex but still critical secondary social behaviours) in a small hunter gatherer pack essentially - all picked up subconsciously from the social environment.
The important difference is that all of this acquisition is a result of tens of thousands of years of consistent natural selection. It's hard-wired because humans have needed these things, and children have needed them as fast as possible, for a long long time.
The things humans attempt to learn in modern times however (non-native languages, formal systems of logic, the ability to argue and reason in complex fashions, the ability to program complex systems) are completely evolutionarily unprecedented, and the result is clear: children are not able to acquire these behaviours effortlessly. They don't just rub off. Instead they (generally) require focussed, extensive supervision and tuition from humans that have already put in the hard work of mastering them.
So the relevance of neuroplasticity still seems small to me.
> The things humans attempt to learn in modern times however (non-native languages, formal systems of logic, the ability to argue and reason in complex fashions, the ability to program complex systems) are completely evolutionarily unprecedented, and the result is clear: children are not able to acquire these behaviours effortlessly.
At least in the case of non-native languages, while it may not be "effortless", every study I've seen has indicated that it is much easier for children to learn them.
