Sorry for the late answer, and sorry for the lack of pictures: I originally noticed different qualities in aging at university, where amidst many examples of terrible aging one lecture hall building and one office/former residential stood out. The lecture hall had a broken rib surface like one of these https://www.reckli.com/en/products/concrete-patterns/ribs-wa... (e.g. "Sicilia") on the larger surfaces which turned the staining of time into a feature, the office/former residential was a framework of concrete (probably modular), filled in with grey sand/lime bricks of similar brightness, but slightly warmer hue than the concrete that gave it a subtle elegance (in my eyes, others hated it) that seemed to be immune to aging.

Not exactly an example of aging well, but nonetheless deserving of a honorable mention: all the old Flagler Hotels that now form Flagler College in St Augustine. They were pretty much making up the modern use of poured concrete for houses as they went and it does show in many places. Most of the concrete surfaces are looking rather rotten by themselves (despite what i suspect to be quite intensive maintenance), but the crazy playfulness of all the decorations that surround them do a surprisingly good job at distracting from that. You notice, but you don't care.