df <- tibble(
DOB = c(19644, 29571, 19744, 22557, 28258, 24366)
)
df_2 <- df %>%
mutate(DOB = DOB %>%
as.character %>% # First convert the factors into character strings
as.numeric %>% # ...and then to numeric days since origin
as.Date(origin = "1899-12-30") # ...and finally to a date
)
# Note: for Excel on Mac, the origin is "1904-01-01" because Think Different.