hmm. I didn't think it was the language learning. However, I don't actually remember the reasoning on that one. Adolescent psychology has been much more of what I've done, particularly in recent years.

ETA: this prompted me to go and try and look this up. Reasonable summary at https://qbi.uq.edu.au/brain/learning-memory/why-you-cant-remember-being-baby. Could do with better citations, but it roughly covers the various stages, and the current state of hypotheses on why neurological development has those effects on memories.