[UPDATED] - Kevin Chan
It really depends on what you consider as the border between child and adult.
I personally believe that it is for people of all ages because there are elements in the game that some kids do not know or understand. Strategy for one thing has always been fit for the faster mind that us adults excel at.
The learning curve is so steady enough that kids can learn it quickly and adults can settle in easily. For those of us who were playing Pokemon Red, Blue and Yellow a.k.a. first generation, we realize just how complex the game can get, especially with the release of the fourth generation (if you haven't experienced third generation), it further complicates many of the aspects we understand about the game.
For example: In the fourth generation, Quagsire (a water and ground attribute Pokemon) would be able to absorb water-based attacks because of Water Absorb ability whereas in earlier versions, it will receive damage from water-based attacks. At the same time, due to its ground attribute, it renders all electrical attacks useless even though its water-attribute is weak against electricity.
Combine this with simple stat builds and you got yourself a ton of both Micro and Macro management, but kids would never understand that, moreover if you try to explain to them this concept, they'll simply get bored and doze off. We, adults, understand that, its part of our experience as workers and gamers.
Therefore, saying that Pokemon is for kids is an act of ignorance and arrogance. If you look deeply, Pokemon is more than just cartoon characters and ultra-cheesy villains and dialogues. It may not matter much to the real world, but the skills developed from this can help build managerial skills that are beneficial in real life.
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It hasn't been estimated on how many play it, but they said to be millions of people from children to adults.
It's appropriate for all ages, but most adults would probably not take as much of an interest in it as kids.
Teens to teens. Adults to adults,young adults and elders. Young adults to adults,young adults and elders. ect.
The Koopalings are adults, Remeber they grew up in the games as teens.
u've either accidently put a cheat in (as making adults go to school has multiple cheats) or they aren't actually adults!