When you're young and precocious you're taking in everything. You were also emulating given your close proximity to your Adeers, but I'm sure it also has something to do with the positive characteristics that they possessed which you wanted to assimilate and make you're own, albeit in a different way.
Bro, humans are meaning-making machines always creating stories based on their experiences, some of which are based on singular/isolated events. Some choose to re-examine these old tales and make new scripts and others prefer to stick to vestiges of their pasts.
Its good to see you're self-reflective and self-aware. The beauty of being an adult is you can be childlike in terms of your thirst for knowledge while having the executive functioning and cognitive dexterity of an adult.
I think what happens is that we're arrested in terms of our notions of age. I've met kids in their early 20s chronologically who are biologically in their 30s, this has more to do with negative lifestyle. And if we're talking about mental age, we all know people who are emotionally stuck in a certain phase of their life that has long since gone, irrespective of their age. So, you might have presented as older in maturity though you're younger than her.
I see where she is coming from. If we have an old snapshot of her being a toddler and you being a newborn then the gap in age is significantly more pronounced as children are rapidly growing. And it can mean something in grade school, not so much later on in life. But sometimes people are unnecessarily mortified by this. But these people are just blindly following the norm mostly because of coercion, and the opinions of others which factor heavily into their decision making.

Interesting. Probably the accumulation of experiences (some good, some less savory). And environmental factors (familial expectations, one's group of friends), we don't quite live isolated in airtight chambers and our decisions have ripple effects on others close to us. I totally agree that people overlook various factors when forming those demands.