I'm 59 and I went gradually in the last 15 years from barely being able to sit cross legged to now I can't even touch my right toe (chronic groin problem) let alone sit cross legged.

Like criss cross applesauce or just one leg over the other?

Istr that there's some genetics involved in which way your legs like to bend. I've always bent easily in that direction. I can sit in full lotus easily or e.g. sit on in the floor, legs ahead with heels together and bend forward and rest my forehead on my feet. And there's many stretches that do nothing for me because I run out of motion before anything gets tight. But legs wider apart, I can almost not sit upright at all. I'm not a flexible person over all.

It's kind of hard to describe, but anyway. Took me until I was many many years old until a yoga instructor told me it kind of varies from person to person how easy some motions are.