Different civilizations have different calendar system and Jesus was born 4 BC if we go by this account. Romans had their calendar, Jewish had theirs, Chinese and Islamic calendar, so what year we're in depended mostly who you were asking.

How Christian calendar became more predominant is due to Western conquest and imperialist expansions, subjugation of other people and lands to conform to western customs.

From scientific aspect, the earth is 4.5 billion years old and from evolutionary perspective, human age goes back much further than 2020.

l would say that a good calendar would began from 5,500 years ago, when writing and written history was established