Just about everyone bicycles in København, young, old, rich & poor. And why not? It's environmentally sound, it's healthy, it's fun. If the sun is shining it's like flying, if it's raining--well, you dress for the weather, because it's a lifestyle, and if you've got good rain clothes you don't even get wet.
The city is pretty flat, not expansively huge, and there are bike lanes everywhere--it's geared to bicycles. It's a lot easier to get around downtown on a bike than in a car, and you have no problem (or expense) parking.
There is a whole industry of bicycle messengers who ride around on super bikes with walky-talkies and pick up envelopes and small packages to scoot them over to another part of town faster than a delivery van could through the convoluted old Inner City, with its walking streets and one-way traffic and lack of parking space.
And if you are a tourist: wonder of wonders, there are FREE BICYCLES to borrow everywhere. The bycykler are parked in racks where you put 20 kroner into a slot as deposit, ride around as long as you want, and when you deliver it to any other rack you get your 20 kroner back again. (Oh, would we have loved to have had something like that in Berlin, where we almost walked ourselves to death, or Paris, just imagine...)