Anyone know about stretching/getting flexible??? Need help!

I myself am a ballet dancer and do a self practice yin yoga a few times a week. My partner was a soccer player and currently does weight training as a means of exercise. He's 21. Very fit. But here's the thing, he can't touch his toes. Not even close! His flexibility limits some of the things he can do. For instance we were staying in Japan for a few months learning about and participating in the culture. In many social gatherings and some restaurants you sit on the floor. But my poor bf can't sit criss cross for more than 3 mins! What the heck is wrong with this guy! He says he stretches after his workouts but idk I know there's something more that can be done. Something better. He complains about his "tight" calves not allowing him to get a deeper stretch into his hamstrings but he obviously has more problems than that. So what do you think gang? Any advice?