I think it's more a feature of being secure in oneself, which is less common being young. I remember when I was young, doing things like eating out, going to a movie etc alone seemed weird. then I did those things and it wasn't. now that I'm an old, I've traveled overseas for months at a time, explored places, moved to new states, and lived entirely on my own in new places and had to find/cultivate an entirely new social circle. it just feels like being independent.
I think in my late teens/early 20s the idea of doing all that on my own was overwhelming, whereas doing things in a little group or as part of a couple seemed much easier.
there are people my age that would find it so even now, but they are probably in the minority. being > 40 and not being capable of many doing things on your own is more the "odd" situation.