I've felt this way for most of my life, and not just two personas, but several. When I was a student, I had my cool, self-defensive persona. When I was home with my parents, I was my quiet, not revealing to much self. When I was out with my friends, I was my fun loving, cut-up self. When I was at work, and I worked as a church organist by the time I was 12, I was a little adult. But I never felt like I was my age. I've always felt younger, even as an adult.
I've usually been in charge of other groups, various choirs and I've had to not just be the adult, but also a leader and one who inspires others to do their best. But I've always felt like I was a kid of maybe 12 years old. I think I know why. I had a psychotic break when I was 12. My parents went bankrupt and we had to move, me leaving my best friend. A part of me just got stuck at that age.
So yes, I agree. We are complex as humans. We have to be not only adults to survive, but skilled adults, leaders in charge, etc. But I'm not sure that many of us want that. It gets thrust upon us, and for people such as ourselves on this site, finally getting home and shedding the adult clothes and replacing them with a diaper and a onsie, can be such sweet relief.