Most cats are considered to be adults at about a year old. One debatable exception is Maine Coons, which grow very fast yet can continue to grow (albeit in smaller increments) up until they are four years old in some cases. So it's no surprise that Coconut, who is a one-year-old Maine Coon, would feel some conflict between technically being an adult yet still having "kitten-like" desires.
Maple's attire (both winter and summer) resembles a school uniform similar to which pop idols wear. Given that she is the only one Shigure allows to choose her own clothes, and this occurred after she decided to give up on that "kittenhood dream," it shows that she still has a desire to be a great singer.
The premise of the series is about catlike humanoids living alongside humans. While this just seems like an excuse to write about a world where Cat Girls exist, the fact that the cat girls are still raised and owned by human masters and can't go anywhere without them until they earn bells to wear is actually kind of unsettling if you think about it; this basically implies that despite having human intelligence, they're considered an inferior species to humans. The creator of the series seems to be aware of this to some extent, as she's asked people not to think too hard about the premise and just enjoy the cute cat girls. This Anime Feminist article takes the inherent fridge horror of the premise and mines it for comedy.
The nekos’ animal like aging. Since they age faster than humans, that means that they're probably in constant pain thanks for the fact that the human body never meant to condense 18 years of growth into a single one at best. And this also means that they probably have to deal with their mortality sooner than we humans do.
The neko's status as second class citizens actually makes sense, based on the mechanics of this universe that have been revealed so far. The bell test is a good example. What is required to pass the bell test? A demonstration that a neko understands the world at least on an elementary school level. Nekos may have human level intelligence, but it's closer to a child's intelligence than an adult's. With that comes poor impulse control, gullibility, and a lot of potential danger. That said this brings up a whole other can of worms in the form of child labor laws, and I'm not even going to touch the 18+ stuff.
Not to mention that plenty of fans who actively look past this to keep the game more butterflies and rainbows with sex.
Nekos are a One-Gender Race; there are no catboys. They also pointedly cannot reproduce with humans. So... where the hell do they come from...?note The answer, according to Word of God, is that there are catboys, we just never, ever see any.
Seems that this will be rectified with the new game slated for summer 2021, with catboys finally getting the focus.
An ID card with a serial number, similar to a Social Security card would make a lot more sense than a bell. If a Neko forgets their bell/card, they could recite the serial number to a police officer, who could simply look it up.
Anime Feminist article takes the inherent fridge horror of the premise and mines it for comedy.