I think the term is "arrested development" but I also think you're way more emotionally mature than 9! So I don't think that label suits you at all!

There could be a normal reason. Like at age 9 you might have been given more responsibility and you matured much faster than peers at that time. You may have looked at the world differently, with more wisdom, more understanding, and the perspective has stayed with you because it served you so well.

There could be a trauma reason. In cognitive psych they talk about how the human brain has a memory spike from about age 18 to 25 where the mind takes in a great deal of information into long term memory storage (Memory slowly, continually declines after 25). At no other time in our lifespan is our memory working this sharply. It's an evolutionary feature, when cave people needed their wits about them because that time was prime time in their lives, they'd only live into their 30s. They needed to be alert, they needed to know where to get the food, and they needed to pass that down to others. It's also the reason why some people seem to be stuck at that age emotionally. For instance, they only listen to music from that time period, they don't embrace new fashion trends, they don't pick up new hobbies since college, etc.

When you add trauma to the mix, you turn on this alertness early. You're amygdala is hyperstimulated, you're experiencing what certainly feels like a life or death situation at an age where it's supposed to be unheard of. I feel like that could explain why one place in time seems like where it all happened. Your amygdala might have switched on hyperdrive and said, "Holy cow, pay very close attention or we'll never get out of here in once piece!"

I often feel like everything happened when I was 12 and a lot of bad things did, but the trauma started much much earlier. I think 12 was when I finally couldn't pretend anymore like it was normal or acceptable. I was mature enough to know it wasn't, and the only way I was going to make it any further was to compartmentalize, turn my anger and loathing inward, and deny it.

I go back and forth, sometimes I feel like I never grew up and sometimes I feel like the oldest lady in the world. But I don't feel my age. I never feel my age.