Research on the “best” ages for English Language Learners (or for anyone to learn a second or third language) is a bit mixed.
I’ve shared various studies over the years, but thought readers might find it helpful if I brought them together into one post and start adding to them.
Here’s what I have so far (please suggest other resources):
The age factor in language learning is from The Language Teacher Toolkit.
At What Age Does Our Ability to Learn a New Language Like a Native Speaker Disappear? is from Scientific American.
What is the best age to learn a language? is from The BBC.
Younger is not always better when it comes to learning a second language is from The Conversation.