Dual nationality holder and live more than 15 years ouside Japan

I am a student going in summer vacation to Japan for the first time and go back, is it possible to use Rail Pass during my visit. May I stay more than one month and during this period I would like to make a tour in Japan.
Is the date of rail pass ticket open ? Because I do not know when I will start my tour after arriving Tokyo.

Thank you in advance for your cooperation.

Nesma Ogawa