Tobi_444
In my opinion, based on the reactions of hiruzen and the three stooges. That the best way to explain his power at such a young age is that they do a dna test when he goes back to the village after the war. Because of having tobiramas template he became biologically a senju. It gives him tremendous backing a resources to continue getting stronger, and as a bonus tsunade learns that she has another family member alive so she doesn’t leave after the war.