[quote=Yog Sothoth]
Also how did he acquire the sharingan? The eldest son had a spiral version of the rinningan
[/quote]

[quote=IVIasterJay]
If we're going to go that into depth in regards to canon and continuity, then the sage's eldest son should have two children, the eldest of the two with Byakugan and the youngest of the two with Sharingan. The Sage's eldest son held both dojutsu as his KG, which separated into the Byakugan KG and Sharingan KG in each of his two children, at the absolute earliest.
[/quote]

Because he's Uchiha and the Eldest actually had a dojutsu that was unknown in power.