There are 2 questions you need to know before understanding who the target audience is specifically. The first one is who are the actors. The second is your particular use for computers and the knowledge you have to use them. First we'll talk about the actors playing the Mac and PC characters. The actor playing PC is John Hodgman and he is an unknown actor who starred in nothing former to this commercial. The actor playing Mac however is Justin Long who is well known for many movies such as "Galaxy Quest", "Jeepers Creepers", "Dodgeball", and most famously "Waiting.". There is one thing in common with all the movies listed; they are all targeted toward the 16-26 age demographic. With that information we understand why the Mac is dressed as a high school or college student because students need new computers for school but they aren't the only target audience. Anyone who doesn't understand how to use a computer or is generally frustrated with using computers is targeted by Apple. Saying Macs are "better" and "easier" is a simple way to attract consumers who find PC to be too complicated. These general terms are simple to comprehend and that's exactly what Apple is trying to do with their products and commercials.
Apple has set the bar when it comes to simplicity. They try to make every product, feature, name, and advertisement "simple" so what better way to show this than a blank room with 2 easily understandable characters? Just from the looking at the PC you get the idea that he's a businessman his demeanor, hairstyle, and oversized glasses say that he wasn't the most popular kid in school. The Mac however looks like a laid back, younger generation, trendy guy. When you look at these 2 in the same room, the color contrast alone shows who you shouldn't listen to. The blank white room exaggerates this contrast and helps you focus on who to side with.
