Do you have a source for that? It’s something I’ve always believed, but have never seen actually rigorously researched. I’ve long suspected the “adult language

Do you have a source for that? It’s something I’ve always believed, but have never seen actually rigorously researched. I’ve long suspected the “adult language learning difficulty” is simply due to having less time as you get older (not to mention an often ossified/obstinate attitude towards learning something new from scratch and feeling clueless).