This album is super catchy, great for singing and dancing and having fun in general. They have music for everyone, like slow ballads (Little Things, Summer Love), songs to rock out to (Rock Me, I Would), and everything in between!
One Direction appeals to all ages in different ways. There is lots of One Direction merchandise for younger kids and tweens, so it seems like they are targeted towards that age group. However, their fandom (the Directioners) are mostly teens and older, and therefore have the ability to be more connected with the band through social media, which the band uses quite a lot, like Twitter during their concerts.
The boys in the band are from about 19-21 right now, so they are definitely evolving their sound as they grow older. However, younger kids will still like it because their songs are catchy and have a good beat, although they may not pay any attention to the lyrics which sometimes can be mature. (Rock Me for example: I want you to hit the pedal/heavy metal/show me you care), but they don't swear or talk about drugs, drinking, or smoking. There is minor language! Muffled in the background of "They Don't Know About Us", one of the boys says "Dam* girl" more than once, but that's the only occasion where they sort of swear.
Although they are choosing to have tattoos and such, they still are good role models. They are polite, respectful, and still pretty clean-cut, although they are going down the route where their sound is going to become edgier and more pop-rock. Sometimes in their interviews, they get cheeky and sometimes swear during concerts, but not very often. They are teenagers, don't forget!
Their songs are still super catchy and fun, great for singing along to. They always have good beats and don't include rapping or a lot of dubstep if that's something you don't like.
As a fan, I would advise others not to get too swept up into their fandom. They have lots of merchandise, some of which is more enticing than others. For example, they have a new perfume called "Our Moment" and lots of official t-shirts and the like that are a little overpriced. Fan-made items or DIY's for One Direction inspired items are out there, so I would reccomend purchasing those if the official merchandise doesn't appeal to you. They have a world tour right now and one coming up, and tickets are much, much sought after and resold for tons more, so keep up with their ticket information if you think you would like to attend one of their concerts.
The fans themselves use lots of social media and are pretty amazing. They make beautiful fan art that you may enjoy looking at or have cool remixes and mashups. However, they are sometimes more mature and aren't afraid to swear or include sexier or racier comments on their blogs, twitters, etc. so watch out.
Overall, One Direction is a fun boy band that appeals to pretty much everyone, but just stay wary as they are older and have an older fanbase compared to what you may think.