I think I am basically 95% bilingual, my native language is not English, but it was thought in school from first grade (age 5 or 6) all the way to high school (17 years old), and then in post-highschool education, I also had 2 mandatory English courses. The thing is having learned so early is I was too young to realize when I could start entertaining a conversation in English without thinking because it was almost always like that for me.

I do think though that when you can think in your 2nd language without having to mentally translate in your head to your native language is when you’ve reached a level of fluency that is good enough to be called bilingual