Several centuries span the distance from the fall of humanity until the Flood. It appears that God’s decree to humans concerning diet did not change until after the flood of Noah’s day.
Apparently, humans were vegetarian during this era. (See Genesis 1:29-30, 9:1-4.) If they were allowed to eat animals for food before the Flood, there is no specific reference of it in the Bible. This does not mean that we have to be vegetarians today.