As I've previously noted, it's a widely held stereotype that children can learn easily, but adults find it much more difficult. I've never found good compelling evidence to support this view when searching for exactly that topic. Trawling through more general neuroscience reading I found a strand of research that has sought to address exactly this area.
This paper by Knowland and Thomas gives an interesting and useful perspective on adult learning. This earlier paper by Thomas provides a good overview of brain plasticity although the differences between adult & child learning are not made very clear - the Knowland and Thomas paper does a good job of clarifying that.
The basic summary is
- synaptic pruning does reduce some learning capabilities during and after childhood, but these are structurally basic abilities like auditory discrimination of phonemes (there is possibly an interaction here with music & instrument learning. Anecdotal evidence from instrument teachers suggests that the ability may be retained/regained in later life for instrumentalists. The 'Perfect pitch' ability is also relevant in this context)
- adults learn in a more attentive & focused way. That doesn't necessarily mean structured, but attention is required rather than entirely passive absorption.
From a language learning & neuroscience of adult learning point of view, the publication output of Birkbeck College has turned out to be an absolute gold mine. I'm going to be reading their papers for months.
'Developmental Cognitive Psychology' - Mark H Johnson.