Other ways to say "native speaker"

Are there other ways to say "native speaker" which also allow a bit more flexibility as for when the speaker learnt that language?

A child of an immigrant family who moved to the US when he/she was 5, for example, who speaks fluent and flawless English now but English is technically their second language nonetheless should be called what?

I understand that I could still just call them a native speaker. But to me, and I don't know exactly what it is, but just something about the word "native" doesn't make it sound quite right, not wrong either, but I feel like there could be a better way to say it.

Something like a "fluent speaker" could do the job but it can also be used to describe someone who learnt the language as a completely foreign language and just became fluent in it, which makes it not appropriate for the purpose I'm trying to use the word for.

So by "flexible", I think I mean what do I call somebody who's basically been speaking that language for their whole life? Whether it was technically their first language or second.

Edit: I understand it’s not incorrect to consider this child a native speaker. But it’s that “not incorrect” part that made me ask this question. If I use the term “native speaker”, I feel like it kind of requires me to specify what I’m counting as “native”. So I was wondering if there was a term that would immediately let people know the level of flexibility I’m allowing/implying without me having to specify it

I'm afraid this child is, in fact, a native speaker - since the language is already hardwired in his/her brain. I am aware that the word 'native' relates to origin by birth, but in the case of languages, the word 'native' is closely related to how deeply intrinsic the language is in one's life and culture.

There are the language specific names such as Anglophone - fluent in English, Francophone - fluent in French. According to the OED these can be used both as nouns and adjectives. However they can be applied to non-native speakers as well, such as language teachers and students, translators and similar.