Q: How old are the ponies?

The ponies' ages were left intentionally undefined. I like to think of them as having maturity levels anywhere between 12 and 18, (but remember that maturity is different than age. You can be a 10-year-old with the maturity of a 15-year-old, and you can be a 35-year-old with the maturity of a 15-year-old.) For story telling purposes, they needed to be able to live independent of parents, but innocent enough for the type of lessons they learn at the end of the episodes. Since horses are full grown around 5-ish, I guess I sort of justified it in my head that they could be childlike young adults. I know this answer is frustrating for some people, but it happens often in cartoons. How old is Bugs Bunny? Mickey Mouse? Sponge Bob? I don't know either.

Q: Is Equestria a planet or a country?

I imagined it as a country, but beyond that it is left intentionally undefined.

Q: Is it Derpy Hooves or Ditzy Doo?

It sounds like it's finally landed on Derpy Hooves, but you should ask the current show runners.

Q: Will we see more of {any given character}?

I can't answer this one—— you will have to wait and see!

Q: Is "Octavia" Pinkie Pie's sister?

It was never planned that they would be sisters. The color similarities, I believe, were a coincidence. I would say no, they're not sisters, but I don't know if the current show runners have other ideas.

Q: Where are Applejack's parents?

To put it bluntly, we just never figured it out. I just liked the feeling of them living with their Granny, but keeping the family dynamic tight and small. To be honest, I would like to simply say that they passed away somehow, but it's just it would have likely been deemed too sad for a kids' show and I don't think it would have ever been approved. There was brief discussion of them being traveling salesponies or explorers, but since we never needed the information in an episode, nothing was ever made official. So it will have to remain a mystery until someone decides to define it.

Uh, Rich, Claire is 12.