How long did God say man would live according to the Bible?

In the beginning, mankind was meant to live forever. When Jehovah God told Adam about the Tree of Knowledge, He brought out that he would die...but only if he partook of it. (Genesis 2:16-17) Therefore, if he didn't eat from it, no death. Add that to the fact that Jehovah "put eternity" in man's heart, meaning that we have the innate desire to live forever. (Ecclesiastes 3:11)

Adam and Eve chose the wrong path however, and that's when imperfection (which brings death) was introduced to the rest of us. (Romans 5:12 & 14) Thanks to Jesus' sacrifice however, if one exercises faith in it they'll be able to attain eternal life in the future. (John 3:16; Romans 5:18)

(New World Translation of the Holy Scriptures)