Maybe minato is part senju, it would explained his ability to learn FGT and how is son is similar to 6 paths as noticed by the juubi. Possibly his dad could have been namikaze and his mom senju or uzumaki?
Naruto resembles The Sage for his acceptance of the Biju and mastery of Biju Mode, and for being an Uzumaki with the chakra reserves to handle it all. Data relating to the manga pages (which bumps it up to "more than speculation") suggests that The Sage was an Uzumaki to begin with, which means Minato doesn't have to be a Senju or related to Senju to have this effect.