Yes and no—the whole discussion is actually two discussions, I think.
One is about in-principle possibility, the presence of something like a critical period, etc. There it is crucial for confounders.
The second discussion is about in-practice possibility, whether people starting later can reasonably expect to get to the same level of proficiency. Here the “confounders” are actually part of what this is about.
Yes and no—the whole discussion is actually two discussions, I think.
One is about in-principle possibility, the presence of something like a critical period, etc. There it is crucial for confounders.
The second discussion is about in-practice possibility, whether people starting later can reasonably expect to get to the same level of proficiency. Here the “confounders” are actually part of what this is about.