Buy it only once you hit 50, it's good if you have a wealth of experiences to overlay its insights with - else it sounds preachy. It was written pre world War 1 so pinch of salt since it's an excercise in hypotheticals and common place observations - doesn't hold up to the modern readers experience of (at the bare minimum) anecdotal driven self help books
Easy to finish though, if you are into it. 20 minutes read for rhe convinced and 45 minute stilted read for the unconvinced