It is a very realistic and great simulator, but With realism comes real-life complications. For very young kids, they won't be able to understand the game well enough to enjoy it. However, if you're old enough to understand aircraft systems, etc., you can enjoy the game
This game shouldn't be rated by age, it's just how much you know about aviation. Yes, i do know a lot about planes, flying, navigation, everything. a 7 year old could play this, he/she just needs knowledge.
MS Flight simulator X is a very realistic and well made flight simulator, but like all simulators it is extremely complex, and pointless for anybody under the age of 14ish. However, before you buy this product consider an alternative: FlightGear. FlightGear is a more powerful simulator that allows advanced users to share self-built planes and maps, allowing a virtually infinite amount of content. The best thing about FlightGear? It's completely free. However, it is a very complex product and really is only appropriate for 14s or over.
I have been playing this game since 2007, and it teaches you about aircraft and how amazing they are. Free flight is for anyone, but if you want to do the more complicated missions, you actually need to know about plane systems and how it works.