When did Barbie collecting start?

These are the copyright and dedication pages of the book The Curious Clubhouse.

I've wondered over the years when Barbie collecting became a hobby.  I think I've found an answer.  It's much earlier than I thought.
I've acquired a children's novel called The Curious Clubhouse, by Christine Govan, copyright 1967.  I read this book as a girl and enjoyed it, and when I saw someone had placed a nice hardback copy of it in the local Little Free Library, I grabbed it.
I'm assuming Govan wrote the book in 1966 and it was published the next year.  Nothing indicates that the book was revised in a later printing (if there was one), and that the dedication might have been rewritten in future editions.
Note the long list of items that E.D.W. collects--including Barbie dolls and doll clothes!  This was in 1966!  I sure would have liked to have seen what she had obtained in those very early years of Barbie's existence!