DC18 was the HG oldest, with DC15 looking as if she were behind in comparison to her brother. She didn't catch fire until she had found an area in which she didn't have to compete with an older, more accomplished brother (academically and in sports).
Growing up, I noticed this as a youngest observing family dynamics of 6 GT+ children as well. My oldest brother was HG and tended to do the talking when the rest of us were born. My HG oldest sister (less than a year younger than him) took over art and creative writing in the family. They were both typical oldest children with respect to achievement and milestones. The middle two GT in our family definitely have middle children traits--being lost and not "achieving" until they found their passions. My GT brother definitely fit the younger sibling role, being quite intelligent but allowing everyone else to express what he needed or wanted to Mom and Dad or relying on siblings to figure it out eventually. He always has been less academic than our other siblings and has expressed his intelligence as an EMT. I was the only younger sibling (PG) noticed as GT by comparison to my oldest brother.
