Who's the adult here?

I wanted to catch up with another good friend of mine, while I'm here. He was kind enough to invite my visiting mother and me out for breakfast. I passed the invitation along to her. "Great," she said. "What should I wear?"
I thought it was a great idea too. After all, my Mom is only 18 years older than I am. And she spends way too much time at home anyway.
So, we meet this friend of mine. I introduce them. He gets us muffins and lattes, and we sit down to munch and talk. My Mom asks a couple of questions,I interpret back and forth, but then my friend and I start speaking fast English about mutual interests. It was just the next natural thing to do. Before I could even get to half of the things I wanted to ask him about, my mother is done with her muffin and coffee, she's falling into boredom and starting to play with my cell phone. A message arrives while she's peeling this navy blue rubber coat off the back side of my cell, and she is asking me how to reply. Then she's typing, asking questions again, all while I'm in the middle of a conversation with another person. Wait a minute?! Isn't that exactly what she taught me was rude?
I was in an awkward situation myself. I started realizing that this was not such a good idea. I mean, I wanted my mom to meet this friend of mine, and he wanted to meet her, but I forgot that they will not have anything to talk about after the first five minutes.
So she's now calling M. I glance at her occasionally. I ask if there's anything she would like to say. "All I want to know is can he get you a job?"
When do parents start behaving like children, and vice-versa? Is it when you turn 30?
I mean, my Mom was behaving like a bored six-year-old, while I was trying to have an adult conversation. She even admitted that we've switched roles afterwards. I also complained later that she didn't even try to listen to what I believe was a very stimulating conversation, and that all she cares about are the house and having grandkids, and she didn't even try to deny it.
I guess somewhere along the line I deserved this kind of treatment. I'm sure I've stopped and rushed her from many adult things she wanted to do. But I always thought I'm safe until I have my own kids. Well, think again.