This is my understanding too. Historically we refer to time periods where life was different. People in the 1500s lived differently than people in the 1800s. It’s mostly technological advances that separate time periods. There used to be large gaps of time before technological advances caused changes in society, but that isn’t the case anymore. The 1980s were much different than the 2010s. People who were born in those time periods have much different life experiences even if they’re close in age.