Hi Noah,
Thanks for your question.
The first five books of the Old Testament were written by Moses probably somewhere in the 1400's BC. Other prophets wrote subsequent Old Testament books at various times. Isaiah, for example, is thought to have lived in the 700's BC to later 600's BC, so that's when the book of Isaiah would have been written. The last book of the Old Testament, Malachi, was likely written in the neighborhood of 450 BC. The New Testament books were penned over a span of time from about 50 AD to about 100 AD.
Thanks for your interest.
Bless,
Ken