What you use and how you use it has a lot of factors besides age. It has to do with your friends, their friends, where you live, what school you go to or what job you have, etc etc.
I'd like to share an anecdote about umwelt. A few days ago, I walked into a coffee shop. I sat in that coffee shop for two hours.[0] When I first walked in my jaw hit the floor as I scanned the room. Everyone had tablets, young, old, there was no common pattern. There was one person I could see reading a physical book, and two graphic designers in the back with Macbooks. My first thought was "Either I'm living in a bubble, or coffee shops are a bubble.".
I figured that if this is what it looks like in suburbia, then it must be even crazier elsewhere. That's when it hit me. If silicon valley developers do their work in coffee shops, and all they ever see there is mobile devices, then they'll naturally develop for mobile devices. But then mobile is new, hot, and growing all the time. IIRC mobile sales have already outdone consumer desktop and laptop sales.
Are developers choosing mobile because it's new and big, or because they see it in coffee shops all the time? Probably both. They're not exactly mutually exclusive. Just like how you have to ask if consumers are switching to tablets because laptops are too bulky, or because they're more usable, or because that's where the focus of every up and coming developer is right now? Probably a combination of all three and more.
All of that might have seemed pretty obvious to you. Well it wasn't to me, heres why:
1. In my circle of friends, everyone still uses desktops or laptops. Having only a laptop seems to be a result of financial concerns, not a lack of demand for a desktop.
2. At my school a handful of people have tablets. Me being one of them. A group of kids asked me what kind of cellphone it was when I first used it in class.
3. Among my friends Facebook seems to be the dominant communication medium, alongside telephone services. I only use the latter.
4. My school has uncommon demographics, The vast vast majority could be described as one or more of the following: Nerd, Hipster, Extreme anime and manga fan, Gamer. So I guess I myself sort of live in a bubble. I don't even own a cellphone.
I live on the west coast of the US. Not exactly a remote location.
[0]: This was the first time I've ever actually sat down in a coffee shop.