Age demographics are very important for countries and cities. Due to the nature of demographic trends, there are a ton of people 20-35 in the USA right now, more than there are "baby boomers". Due to the similarities in taste due to age, many, many, people want to live in cities right now, which drives gentrification. Whether or not that continues probably has a lot to do with birth rates going forward for people 20-35.
What are the age demographics of Canada?