Your tutor got that wrong, Providing you have no physical disability, you will continue to improve your flexibility.There are exercises on this site that address this issue but, right now, I can't point you to them.

I'm sure someone will come on and guide you in the right direction.

If your tutor got this wrong, where else has he mislead you?

Guitar Tricks will always give you acurate information and their tutors are second to none in my opinion.

Joe