I think if u were educated in SG, u should have finished up being at least bilingual to some extent, even if u went to an English School from the 70′s thu to now. It is common for many School kids & teenagers today will tell u “I HATE CHINESE”, but they are in fact quite capable of Conversing smoothly, & reading (albeit slowly) at least some Mandarin material (not so much Newspapers but entertainment magazines etc)

The only classmates I have who manage a C6 or worse in CL2 are Chinese Peranakans. They have no contact whatsoever with the Chinese Lang. at home, but more significantly is their attitude towards learning the Language. When writing Chinese essay, they would argue & insist that Chinese sentence structure should be the same as English Grammar E.g. I want to improve on my Chinese 我要进步我的华语, much to the exasperation of the Chinese Teachers.

That being said, I guess it is always better to be late learning the Lang. rather than not having learnt it at all. You learn best when u develop an interest. Happy Learning
As for me, I have long lost my writing (w/o dictionary) capability thru yrs of dis-use of that skill in SG & Oz after graduating.
My Prof. in Oz even jokingly questioned my A1 Chinese proficiency stated on my CV, to which I sheepishly agree, was no longer valid! Classic Case of USE IT, or LOOSE IT with Lang. Skills

Yes let’s hope it’s not a reflex action that charts the near future!