Ok, i consider myself competent 3 languages(English, Tamil, Hindi). And all three are as different as languages can get(grammatically,lexically). I consider myself C1 competent in only English. I suspect i might be able to clear it in Tamil as it's after all the native tongue, though not sure, can do it without a month's studying(part-time). My experience, I learnt tamil and english during my school days. (english being the medium of instruction). I was fluent* in both in my teens(can't remember much before that, except what seems like episodic memory reformed by hearing). Somewhere around the age of 11/12 i started to learn hindi. but i achieved fluency quick. Infact one of the repetitive grouch/feedback i got from teachers' was "don't write on your own. just reproduce what you read. Newton's law is newton's.". Ofcourse I used to think if you want Newton's words go read the textbook and not my answer sheet.

-- I know i scored a 287/300 in TOEFL. Don't know of any equivalent in Tami l/Hindi, that i would compare to that format.

*-- I mean fluency in terms of forming sentences, by combining vocabulary learnt with/without context to form sentences that express and/or describe processes. Not spoken competency. That came long after that, only when i was forced to immerse myself(school rules around 16 for English and later at 25 when went to do a Master's for Hindi).