Michele Daigle The book is more erotica than self help if you were looking for curing a fear of flying.
Lizzie I read it in 1977 when I was 18 and in college. Some of it made more sense a few years later, after being married a bit. Response and appreciation of this book has more to do with experiences than with age
Lobstergirl Ages 13-28. This should be read after "Forever" by Judy Blume is not titillating enough for you, but before you actually know a huge amount about relationships.
Sierra This book is appropriate for any age group but is especially important for women in their early-mid-late twenties. I am 21 and I am glad I read the book when I did. It brought a voice to the issues that have been swirling around in my head surrounding femininity and marriage. Although it was published in 1973 (I think), it is still relevant today.