It is one thing to improve the IQ of rapidly-growing children who have developmental disorders, and quite another to improve the fluid intelligence of adults.
The author does mention this under '2. Challenge Yourself':
> I'm going to shatter some of that stuff you've previously heard about brain training games. Here goes: They don't work. Individual brain training games don't make you smarter—they make you more proficient at the brain training games.
Brain training games don't boost IQ http://www.vox.com/2016/6/22/11993078/brain-training-games-d...