If you prefer guys in their late 30s and 40s, you should also consider Jinya, which is a 24-hour sauna, (similar to 24), considering of 4 storeys. If I am not wrong, the entrance fee is 2,400Yen for 24 hours and you can stay overnight at the place. During weekends or weekday nights, there are lots of actions there too. It is located at Ikebukuro area. If you are in Shinujuku area, it is only 10min JR train ride, followed by another 10 min walk.
For directions on how to walk there, you can PM me or refer to the utopia-asia.com website.