[@Hael] those levels are just up there as a guide to how many khookies are required to level up, rather than as a limit. There is no limit on levels.
It's just to establish that the pattern of khookie requirements is as follows:

5 -> 6 -> 9 -> 10 -> 15 -> 16 -> 19 -> 20

Goes up by 1 (5 to 6), then goes up by 3 (6 to 9) then goes up by 1 again (9 to 10) and so on.