This is really fine article. I agree with its overall sentiment that it's difficult to draw hard lines.

Answering the question posed in title - I have no idea.

When I was a kid, I thought that person becomes adult in the day of their 18 birthdays.

But being 18 years old, I didn't feel so mature. "Maybe when I finish university", I thought. But nope, it didn't feel like being adult.

Maybe when I have a stable, "real" job? Nope.

Maybe after I leave my parents home? Still not.

Maybe after marriage? It's still not that.

I suppose I still consider being adult with being serious, busy, and in total control of their lives. And I don't feel that yet, probably I will never will.

I feel that this view of adulthood is a bit childish. And most likely I never will feel adult in this specific way. We never are in a total control of our lives.

But - do I feel more mature than in my 20'? Of course I do. I have much more responsibilities. My decisions and my actions are much more deliberate than they used to be.

But I just feel that I still have a long way to go...