In one episode of Bewitched, we see a painting of Samantha (we assume it's Samantha) which is set in old Salem by the looks of it. This then raises the question of how old Samantha actually is, but the question is never truly addressed. So, how old is Samantha at the time of the series (educated guesses are acceptable).
There is a very extensive analysis of contextual clues from the episodes as to the various ages of the witches here
In # 3, Endora makes reference to having known Diogenes (400 BC).
In # 5, Endora makes reference to having known Julius Caesar.
In # 23, Endora says she cooked for the Roman Emperor, Claudius.
In # 24, Endora makes reference to having known Helen of Troy (1180 BC).
In # 160, Serena tells Phyllis that Endora admits to 1000.
In # 168, Maurice says he and Endora knew Atilla the Hun (450 AD).
In # 210, Endora says she has changed her mind many times in 3000 years.
On the other hand:
In # 171, Endora says she went to Shakespeare's plays as a little girl.
In # 175, Endora refers to being a child bride when Samantha was born.
In # 203, Endora again says she was a child bride. This time she defines it as being in 1670.
In # 230, Endora says she was not born at the time of King Henry VIII (1570).
Ignoring the fact that several episodes specifically contradict each other, the general theme is that Endora is at least 3000 years old and that Samantha was (probably) born sometime between 1570 and 1600 which would make her approximately 390-400 years old at the time of filming.