Is it normal to not have your period by age 13?
Yes, it's completely normal not to have your period by the age of 13 years old. the average age of menarche is 13 years old, but anything up to 16 years old is completely normal and some women don't start until even later than that.
The average age of menarche (first period) is 13, but that doesn't mean that you should have your period by the time you're 13. You're still young, you could get your period any time in the next 3 years and still be considered perfectly normal - even if you don't reach menarche by the age of 16 you may just be a late bloomer.