I'm the oldest child out of 4 girls and I'm a submissive. I've always had to take care of the other 3. Especially my 2 half-sisters cuz they are a good 7-8 years younger than me. When their mother died, they were still kids and looked to me for help after that.
That said, the 2 middle girls are both self-centered bitches...lol Now me, and my youngest sister...we are both submissive. Which is kinda weird too cuz of the 4 of us...she and I are the Daddy's girls. Hmmmm...
edit: just noticed..the majority of both submissives and Dominants seem to be the oldest child.