I thought until recently Hillary was Bill Clinton's daughter
What is your impression of the Clintons?
I don't know, I have never met them in person.
It's okay to mistake the relationship between two people. Unless you follow politicians closely, it's normal to not be aware of who they are.
I should have known it's not possible for a woman her age to be Clinton's daughter.
Not everyone has the knowledge about politics as much as others. Now you can just say you learned something new, and then be satisfied with yourself. Age sometimes is just a number.