The world has changed. Back in the 1970s, people got married in their early 20s. Now, if people get married at all, they do it in their late 20s or early 30s. Few 22-year-old college graduates are looking to move to suburbia. Long Island was designed for families, not for single people on the move, or the make. As a result, we’ve seen a dramatic decline in the 20-to-34-year-old cohort that is highly educated, highly skilled and focused on high-tech, creative fields that will fuel the economy of the future.

We need these young people. We need their energy, their creativity and their entrepreneurial spirit. To attract them, we need more “cool downtowns,” with multi-story buildings, affordable apartments for rent, and offices with restaurants and shops on their ground floors. We need the activities and demographic density to stimulate young people’s creativity.

We have a few cool downtowns now, but not enough of them. Rockville Centre, Garden City and Great Neck have downtown rentals and offices and restaurants and shops and train stations nearby. But there aren’t enough affordable apartments. Long Beach, Westbury, Hempstead, Mineola, Glen Cove and Farmingdale are trying to create cool downtowns, but to really be successful, we need more of them. We need to create at least 20 cool downtowns so it will make economic sense to link them by rapid bus and mass transit.

Don’t get me wrong: We all want to preserve 95 percent of what made suburban living so attractive in the first place. Our single-family neighborhoods will stay, and we’ll preserve our parks, beaches and open spaces, but we need to make them even better. We will maintain or even improve on our low crime rates, good schools and quality services, but if we don’t want to go broke, and if we want the vibrancy and creativity and economic power of the next generation to propel us forward and expand our tax base, we need to grow responsibly, in cool downtowns.