It's about time someone wrote a book for those of us "over-the-hill" martial artists. Seriously, though, this is a great reference for any adult martial artist, regardless of age - sort of user's manual for the martial artist's body. And some of the information is very advanced - this is not just an introductory book for beginners. Great insight by the author into what it means to be one of the oldest students in the class.
I hope Mr Kim gets around to publishing a similar work on Martial Arts after 50!!
The book does describe good/safe training practises, but if you are not already following these well before the age of 40, then you are not likely to be still a practising martial artist or any other sport after 40! So, a reasonable attempt but the title is a bit of a misnomer.