Adults wearing backpacks is silly. I think it's more closely related to adults watching "Adventure Time" than My Little Pony. I mean, I can understand the need to carry things. That's what a briefcase is for. In the event that you need to carry more/heavier things than would be manageable by a briefcase, I would go with a nice leather messenger bag.
The My Little Pony thing... google "Bronies". But NOT on a work computer...
I use a ballistic nylon Tumi for my laptop and other crap. It has a shoulder strap and can double as stopgap armor, sufficiently loaded (with kevlar plates, haha). I like the Tumi leather, but my bags get hustled around quite a bit and there's nothing I hate more than scratches, so the ballistic was the right choice for me. It is also impervious to water.
As for the OP, I've noticed it too - and it's kind of annoying. I used to use a backpack in college. That said, these kids will grow up. For example, we had some kid with dreds (or is it "dreads? - a white kid with reddish-blond hair) come in to work. He wore them for a year or two and then, one day, he came in with a more professional look. When asked, he just said, "I just got tired of it."
If you wear a backpack and you're not in some form of school, I can't really take you seriously and will deny you admission to "The booster's club".
My Little Pony... betta than "Glitta My Little Pony". I always figure that, when my little pony chicks grow up, they tend to overleverage on things like houses and weddings, typically ending up in default. I also think they are more likely to make bad decisions regarding tats, aka "tramp stamps", but that's just one dude's opinion. See, it's all about "da pageantry". Don't try to play chess with one of them. They'll line the pieces up like a procession. No, they only have one use, and they're only marginal at that.