Well we know that he was about 14 when he took up the alias 'Tobi'. What i think is that Obito is goal was initially at first about Rin but as he grew older his motives might have changed overtime to something deeper. The reason why i think this is when he was talking to Naruto and co about Lonlieness and talking to them even before the mask came off about making a world where 'heroes don't have to make pitiful excuses in front of graves' (reffering to Kakashi). I think he would know that when Rin is in the dream world she would still be a kid so i think he's actually doing it because he hates the ideals of a shinobi. What do you think?