I'm sure that there must be introverted twins out there, but mine certainly don't make the cut. I don't know if it is just a personality-thing, or if it is the result of being numbers 8 and 9, or being twins, but these two girls like people. They like meeting people. Talking with people. Going places. Doing things. If we combine all these things, they are quite content. (Though content sounds like a much too contemplative description of them.)
I've discovered as well that they are so used to having people stop and either look at them or talk to them, that they are surprised when someone just walks by without a glance. We were out today and an elderly gentleman walked by. G. saw him and I saw her gear up to flash a big smile and her trademark, "Hi!", but he walked by without noticing her. I watched her face and she appeared to be a bit baffled. The smile disappeared and her eyebrows furrowed a bit as she looked after him. I suppose they have to learn the world doesn't revolve around them at some point.
It reminds me a bit of when B. was the same age and he would happily greet passersby with a smile and shout, "Hi people!" It was very cute. A family friend who used to like to take him on walks would get upset at the people who didn't say hi back to him. She didn't say anything to them, but when she and B. arrived home she would be full of righteous indignation that anyone could ignore such a cute boy with such a cheerful greeting.
The moral of the story? If some small person ever says hello to you, be sure to say hello in return. It's only polite.