In terms of classifying something as being part of the "ancient era" persay, most books I've read will either cut it off at the fall of the Western Roman Empire, so 476 AD or end it with a transitional period (late antiquity), which basically spans the christianization of the once-Roman empire, and the "last of the Romans" of Late Antiquity, which is typically considered Emperor Justinian I and the philosopher Boethius.
I'm assuming if you take these dates, then anything before them can be called "ancient," since it would fall in the "ancient era."
Also, this is just in terms of Europe, the Mediterranean, and the Near East. I'm sure there's different dates for other areas, along the lines of local empires. Maybe the decline of the Maya for Central America for example?
some sources/links:
The ancient era according to Minnesota
just another website cutting off the ancient era around 500 AD