1) Общий: Are they about 230 million years old?
2) Альтернативный: Are they about 230 million years old or 300 million years old?
3) Специальный: How old are they?
4) К подлежащему: What is about 230 million years old?
5) Разделительный: They are about 230 million years old, aren't they?