I see that a lot of people wonder what the level cap in Assassins Creed: Odyssey actually is, and the current answer is that Level 70 is the max level. However, this has not always been the case. At release, the level cap was set at Level 50. A lot of users hit that level cap before having had a chance to finish the game, or even the main story, and complained to Ubisoft about it. They looked into it, and shortly after released a patch that raised the level cap to Level 70.
So the level cap is 70 right now, but who knows, maybe they will rise it again once they release more DLCs like they did in Assassins Creed: Origins?