The answer
Calculations from Genesis 5 & 10 and Chronicles could show that man has been around for utmost 4000- 5000 years. However, there is another important fact, namely that the Bible does not mention all the characters and all their ages and that there are gaps in history that are not mentioned in the Books.
For example …
In Matt 1: 8, the genealogy mentions that “Joram begot Uzziah” whereas if we refer to (1 Chronicles 3: 11 – 14) we find that there are three generations that have been dropped from this genealogy …
Joram his son, Ahaziah his son, Joash his son, Amaziah his son, Azariah his son, Jotham his son, Ahaz his son, Hezekiah his son, Manasseh his son, Amon his son, and Josiah his son.
1 CHRONICLES 3 MATTHEW
JORAM JORAM
AHAZIAH
JOASH
AMAZIAH
AZARIAH (UZZIAII) UZZIAII
Another example is the genealogy of Christ in Luke 3: 36 “the son of Cainan, the son of Arphaxad, the son of Shem, the son of Noah, the son of Lantech” … but referring back to Genesis 10: 24 we do not find the name of Cainan “Arphaxad begot Salah, and Salah begot Eber.”
We therefore do not use those genealogies as an absolute method for calculating all the ages and names. It merely mentions the known or relevant names. We therefore cannot just add up their ages to calculate the age of mankind.
Fr. Daoud Lamei