Hmmmm...am analyzing 5 sets of female siblings

Elder Sister versus younger sister.

In all the cases.....there seems to be similarity.

The elder one is pro-establishment, more disciplined, "nice girl", tends to follow a traditional norm...
The younger one is anti-establishment, prone to taking risks, has many boyfriends....

Hmmm.......

Now I forgot the reason why ? Read a detailed analysis in the newspapers years ago, but can't really recollect.