Are there real cases when a person over 20 years old first sat on the twine? Are muscles able to stretch like this in adulthood?

Pfff. A person at 90 can sit on a twine. just a matter of time.

Warmth and work ...

I'm 20, I went to stretching classes, a month later I sat on the twine, although I did not do it in my childhood and never sat on it)

Of course there are! Everything is real. The main thing is methodology, patience, consistency in performing a set of stretching exercises. And everything will work out)