On War and Leadership: The Words of Combat Commanders from Frederick the Great to Norman Schwarzkopf By Owen Connelly.
This book contains the words on leadership from the writings of some of the greatest military leaders the world has ever known.
When I was on active duty in the United States Marine Corps, I read this book cover to cover and have read it again since. This book is a must read for every man but especially for mid-teens to early thirties seeing as how it has so much valuable wisdom to help spring board the potential leadership in a young man.
If you're a 16-30 year old, read this book and study it. Don't be afraid to underline the words and write in the margins of books you're studying; pretty books are nice but used books illustrate a transfer of knowledge so if your reading them, go ahead and make them your own by putting your own notes and thoughts in the margins.