I think the reason that Grandmas have adopted technology at a faster pace is that technology as a whole is becoming easier to use - probably due to a stronger focus nowadays on UI/UX. As opposed to engineers being in charge of design, we now have more real designers in charge of design - see what's happened in spaces like email marketing with Mailchimp. Another obvious example but in hardware is the iPad. Grandmas don't have to worry so much about booting up, operating systems, etc. They just press a button and it works.

I think kids don't blog as much because it's so much easier for them to get an audience through their current social media networks - primarily Facebook. Most blogs don't have huge audiences - mostly just friends and family. So, why would someone create a separate blog and then try to drive traffic to that blog when they can just post similar content on Facebook or Twitter and have it served up to their friends and family? I'm sure they get way more comments on their Facebook updates than they do on a blog anyway. Particularly for a narcissistic blogger, that's what they're looking for anyway - affirmation.