The North American rule of thumb is that young people -- specifically people in their 20s -- are the most likely to to live in an urban neighborhood. After that it's all down hill and, broadly speaking, the percentages decline. But at some point, much later in life, the data suggests that there is a reversal and people start to return to urban neighborhoods, albeit not to the same extent. Part of the explanation for this is that as people age they start to look to more walkable neighborhoods where they don't need to get a car to get around.