I don't think so...Think it back,please...As a recall,who do you think the only characters that live long enough?...This long live characters is the only way to deny the assumption about Tobi is the older son of Rikudou Sennin...Do you guys knows who the hell is the characters that I've been telling to you?...

Yes,the characters that I told,which have been live long enough is the bijuus himself...They live in the world before an Uchiha and Senju clan was born...They live from the days that Rikudou Sennin still alive...They live at the times where the younger son and the older son of Rikudou Sennin fighting each other...They live at the times where the descendants of the Rikudou Sennin sons continuing fighting each other...So,think about it,the bijuus should be knew about the older son and younger son of Rikudou Sennin,right?...There's a times gap between the Rikudou Sennin era until it's an Uchiha and Senju clan era...In that times gap,we don't know what really happens to the bijuus,right?...After all,the older son believed that power and might were the keys to the peace...Who knows,maybe,the older son kept all the bijuus under his control after Rikudou Sennin died...

So,as you can see,none of the bijuus recognises Tobi as an older son of Rikudou Sennin...So,it's make no sense that Tobi is an Older son of Rikudou Sennin...What do you think guys?...After all,this is just my thought...LOL...