Agreed.

Spanish is my first language, English is my second language (age 4), and I've studied German, French, Nepali, Sign, Japanese, and Ewe.

I am considered a native Spanish speaker, meaning that while I also studied Spanish in school, I speak Spanish on instinct, not from having learned it in a book. Interestingly, regionally my Spanish is specifically Guatemalan. And my Spanish remains central american even though I've lived in North America most of my life speaking it with predominately Mexican Spanish speakers, and while I have learned their vocabulary and forms, I've never adopted them.

And while English is technically my second language, I am a native English speaker, and it is my primary language for reading, writing, and speaking.

I suspect we use first, second, native, and primary as terms because of labels used in language learning and questionnaires in the US such as ESL, or advertising that classes are taught by native speaking teachers etc.