I expected the concept of time in a civilization that is quite possibly older than time itself to be different than my own. But I must confess it perplexes me here.
A grand library built in 1998 is old.
A temple built in the 1800's is new.
A hotel built in 2003 is old.
A river dammed in 1955 is new.
A poem written in 990 is.... well, that's Song Dynasty.
Time is not linear here. It's measured in relation to various milestones that shift, some personal or unique to a community. Measured against some things that have not yet happened, hoped for future events.
I don't ask if something is old or new; I ask when it was built or happened. And if dates really matter to you, learn your dynasties.