I think this is all part of growing up. It doesn't just suddenly happen because of a birthday. It takes a long time sometimes.

We start to see parents as less parents, but more just regular people. We get more objective and sometimes discover that this person is not someone we would necessarily be friends with, all things being equal.

I don't know if a strict upbringing has anything to do with it...I suspect it might, as we strive for approval, and being a well-behaved child is all we were allowed to be. It takes a loooong time to be psychologically independent and be okay with that.