This book by Meg Jay, PhD is a must read, even if you aren't in your twenties. Ideally it is for those approaching their 20's and in their 20's. I highly recommend this book to other therapists and counselors.
This book provides anecdotal stories alongside research as to why our 20's matter! So many people spend their 20's wandering, trying to have experiences, avoiding getting tied down, and generally just waiting to get their life together until they hit age 30. The author tries to emphasize how career and relationship choices do matter in our 20's. She emphasizes personality development, and changes in the brain that are affected by our choices. She discusses unresolved issues of identity and social network "keeping up with the Jones's" as potentially isolating or negative information that holds us back. This book encourages the young 20 something to claim their adulthood because when you do you will reap life long positive impacts (higher incomes, satisfying careers, family and relationships, etc). Go read it!