You need the qualities of a king.
Which are multiple and absolutely not problematic as Katakuri, Yamato or Chinjano showed.
Imu is more powerful than them and has more kingly ambitions.
And so? Are you implying that Ryo Is stronger than the whole Goverment?
Apart from the fact that strenght has really nothing so special. Kata was serving BM because she was his mother, Yamato obeys Momo because he Is the shogun son of Oden, etc.
Kizaru's action isn't relevant. Feeding Luffy is a compromise on itself, something CoC users rarely engage in.
The fact that Kizaru doesn't even PERCEIVE himself as someone who rules over the others, means he doesn't have a kingly ambition.
Kizaru's actions are all that matter. And no, Kizaru not only do the opposite of what he said, acting out of his own agenda and will, someting that a lot of CoC users would never dare to, but actually "rules" over a part of the Marine, much like many conquerors.
In fact, you want to talk about kingly ambition? Being an Admiral in itslef Is already a kingly ambition, since It Is the dream of Koby, another (at least very likely) CoC user.
And I am still waiting where Yamato wants to "rule" others (opposite of Kizaru who actually gives orders).