Book is similar in style and elements to "The Diamond Age". World demographics are mostly "old women". They hold most of the wealth and most of the political power. Young people have a hard time competing and/or establishing themselves. There's nanobots, quick and easy travel, lots of single-use items crafted from atom-assemblers, and then recycled when no longer needed. Our protagonist is an "Old Woman" who somehow becomes young again (nanobots, maybe?) She gets a boyfriend, gets a period, freaks out, and gets a wicked craving for some complicated, crosslinked noodles. There's also a dog. He's a genetically engineered messenger dog, who's job is to sniff her out and deliver a message. She refuses the message, which upsets the dog, and makes people angry - because upsetting a delivery-dog is just, mean.
I swear this is really a book and not an acid flashback!