Presuming that cities are meant to be used by people, it stands to reason that their elements ought to be scaled to human comfort, movement, and legibility.
Rather than attempt to describe what architects define as human scale (or at least how I understand it), it may be quicker to pull out two photos I took in Albany, New York. These two places are a short walk from each other.
Although there are technically humans attempting to coexist with this place, they doubtlessly feel as if they are walking across the canvas of a Piet Mondrian painting, ruining its elegant simplicity with the awkwardness of their human bodies. And it's such a long way to walk with nothing to do.
This alley, on the other hand, is one of the streets that the people who work over there go to voluntarily for lunch. They apparently enjoy being here. It has nothing to do with one being new and the other old. It mostly is a reflection of scale.
The tendency to feel at home in places that are designed to fit our bodies seems to be hard-wired. Children are just as much drawn to spaces that are sized according to their own smaller perspective. Over the weekend I visited the Winterthur estate, the museum outside of Wilmington, Delaware that houses collections from the Dupont family. A couple of years ago, landscape architects created a garden on the property designed exclusively for children called the Enchanted Woods. Like J.R.R. Tolkien's fantasy world of the Shire, built around three-foot tall hobbits, the Enchanted Forest has many traditional forms whimsically sized to be experienced by short people. A bird's nest is blown up in proportion as a kind of tree fort , while the cottages and benches are shrunken.
I brought this up to my wife, who knows all about small children, and she understood exactly why they love this place. In a world built for adults, the Enchanted Woods is a place where they can navigate forms that are familiar yet still somewhat alien to them in a much more secure way. This is the same reason why they play-act as adults all the time but need to have smaller tools and settings. Check out any toy store for the miniature lawn mower or playhouse. It's the phenomenon of coziness. It just fits.
I don't think we outgrow this as adults. It just gets a little bit bigger. Many outdoor places today are built around the needs of automobiles, with buildings pushed away from each other and aesthetics meant to capture our attention in 4 seconds as we speed by. In the same vein, they are built for economies of scale or politics of intimidation, such as warehouse shopping experiences that exist for the purpose of maximizing the efficiency of highway trucking networks or the massive squares at the center of every communist bloc city built in the last century. There's a reason why we gravitate away from these places. They just don't fit.