I knew twins who said they started their periods within an hour of each other, could this be true?

Answer 1

Yes. I even have heard that when a group of girls are roommates, they tend to eventually have their periods at the same time each month (unless they are on birth control and that controls it more).

Answer 2

Identical twins are monozygotic. Meaning they come from the same fertilized egg which split. They have identical DNA and will often hit alot of the same milestones around the same time. If you mean that they had their very first period at the same time then yes, this is entirely possible.

Hope this helps,
Mom to identical twin girls