Great game, but very violent for pokemon.
This game is very good, but not suitable for any children under the age of about 5, and due to the complexity of the plot would probably not make sense to most children up to the age of 7 or 8.
I'm pretty sure "Mystery Dungeon: Explorers" is the first pokemon game where one character has attempted to kill another onscreen (and this happens more than once). On a note less related to whether it's age appropriate I think it's also the first pokemon game where two characters (Grovyle and Celebi) are in a romantic relationship.
The words "suicide", "kill" or "die" are never used - only "disappear" is used, but these words would be a lot more appropriate to describe the issues and events in the game.
This game's philosophically very deep, and has some very good lessons in it about morality, self sacrifice and the meaning of life.
It's strange among games aimed at younger audiences (apparently it is, judging by the age rating, even if the game itself is more appropriate for teens) in that good and evil are generally pretty ambiguous. One character (Grovyle) implicitly tries to kill the player's partner, and though he had a reason to do so (needing to escape by any means necessary so that he can save the world) it's pretty extreme for a pokemon game.
Also, if you play this game all the way through, and read all the text, YOU WILL CRY. It's the saddest story I've ever read or seen >>SPOILERS<< in the ending a pokemon watches their best friend (you, the player) being erased from existence, then has to return home and work out how to live without them, then breaks down crying on a beach when they are reminded of everything they have lost, then the credits roll.
This title contains:
Positive role models
Violence & scariness