Second born children can develop more quickly because they see what their older sibling can do and are inspired to catch up and do what the first born child can do. What happens less often, I think, is that first born children look at what their parents can do and then they try to do that. When a child is very young, that gap between what a child can do and what their parents can do is too big to think about bridging.
When a second born child looks at the first born child, it sees a manageable gap of strength or skill. When a first born child looks at a grown up, I think they sometimes see an inconceivable gap of strength or skill, and then they don’t bother trying to imagine that they could do that.
It’s worth imagining that you can do things that others can do. And if they are 5 steps ahead of you, the first thing that you can do is take one step in that direction.
Then another. Then another.