While later age buildings are taller, they don't quite pop enough to show that clearly.That also ties into one of my other major criticisms of the game, the grey / brown sludge that the map turns into when you get urban sprawl. It is very difficult to make out building types at a glance, so at the very least, some sort of coloured roof or flags or borders to signify which type of building is where would help.
I think they need to just add a dim/brightness effect to clearly distinguish new buildings from older ones, and as many have said: some color coding to match function and other visual distinctions.
The BIGGEST problem visually, and this is so endemic of Civ 7, is that the design language requires close up views of the cities, but the game design wants you zoomed out a lot. Talk about inadequate forethought. They came up with a look but didn't design it around how the game is handled and played.
At a MINIMUM there should at least be a camera mode with full freedom of movement to do screenshots and enjoy the visual assets and your unique cities. But the game is very intent on forcing you to see the big brown blob.