I hope my question makes sense. Someone living in say, 372 BC for example. If they died in 347 BC how were the years of their existence recorded? They of course had no knowledge that modern recorded dates would begin at Christ's death (AD).
Your question is pretty broad and there are many answers based on when and where. Do you have a specific place and time period you’re interested in? There have been hundreds of calendars and dating systems used throughout history. Some based on astronomical or historical events like the founding of an empire or the reign of a particular ruler. Many people today still don’t use the Christian based dates. For instance Muslims say the year is 1397. I’m sure someone here can give you a more specific answer about any place and time you ask about.