Few things in sports and fitness are as persistently stupid as the idea that stretching, per se, offers some kind mystical, magical benefit. The entrepreneurs quoted in this piece strike me as complete idiots.
How flexible do you need to be? As flexible as you need to be to do the things you want to do. Flexibility does not prevent injury, improves athletic performance only if it is specific to the sport, and has literally not benefit for longevity or disease prevention.
If you like stretching, stretch. If you are interested in a more intelligent and sustainable approach to lifelong mobility, which is far more strategic than stretching just for the sake of it, then do a strength training (body weight, kettlebell, barbell, etc.) that requires a full or nearly full range of motion and make sure you training opposing muscle groups. And, I promise you this: if you can learn to do the Turkish Get Up correctly, it will change your understanding of mobility.
The New York Times: Stretching Muscles In as the Next Fitness Fad.