1- Oden is obsessed with freedom like Luffy. He always wanted to be a pirate since he was a child like Luffy.
2- Oden has Conqueror’s Haki like Luffy.
3- Oden has the ability to hear the Voice of All Things just like Luffy.
4- Oden has Charisma to attract allies like Luffy.
5- Oden was age 19 when he took over Udon and defeated Shutenmaru like Luffy is age 19 right now taking out the Yonko.
6- Oden became Damaiyo at age 20, like Luffy will become Pirate King at age 20.
7- Oden has 9 Scabbards like Luffy has 9 Straw Hats.
8- Oden causes chaos wherever he goes. There has not been one place Luffy has visited without being in chaos, just like Oden.
Kozuki Clan is 100% a secret D. Family.
*Theory by Rmstorm1