This is a quick easy read for 10 year old through 95 year olds. It is a little different approach than just a factual biography, as the author makes it more of a story line. In any case it is well worth your time to see the way God used this simply faithful man for His glory and the good of 10,000 orphans.
As a 25 year old young adult I was inspired by Mueller's biography as most of his major life decisions started around 25. I bought this book for 7 friends.