Let’s consider that using the Bible and no extrabiblical text there is no certain way to know that meat was consumed prior to the flood. Though there were sacrifices.
However we may be able to consider some passages and speculate.
Gen 4:4 and Abel also brought of the firstborn of his flock and of their fat portions. And the LORD had regard for Abel and his offering
This is similar to
Lev 3:9 Then from the sacrifice of the peace offering he shall offer as a food offering to the LORD its fat; he shall remove the whole fat tail, cut off close to the backbone, and the fat that covers the entrails and all the fat that is on the entrails
And the peace offering was apparently the only offering allowed to be consumed
Lev 7:15 And the flesh of the sacrifice of his peace offerings for thanksgiving shall be eaten on the day of his offering. He shall not leave any of it until the morning.
Lev 7:16 But if the sacrifice of his offering is a vow offering or a freewill offering, it shall be eaten on the day that he offers his sacrifice, and on the next day what remains of it shall be eaten
So peace offerings could be consumed
The idea that prior to the fall no meat was consumed can be deduced by these verses but this does not exclude the consumption of meat.
“And God said, “See, I have given you every herb that yields seed which is on the face of all the earth, and every tree whose fruit yields seed; to you it shall be for food. Also, to every beast of the earth, to every bird of the air, and to everything that creeps on the earth, in which there is life, I have given every green herb for food”; and it was so.”
God did not strictly forbid the consumption of meat and the fact that God sacrificed two animals to clothe Adam and Eve speaks to animals being intended for man and not co-equals with man.
Again the Bible does not explicitly speak against consumption of meat after the fall and prior to the flood. But in regards to the verse concerning the shortening of length of years that doesn’t compute that meat was the cause. After the flood people continued to live for hundreds of years and were consuming meat and animal products.
The reason God shortened the life span of man to 120 years was to limit the number of years man lived without His Spirit
Gen 6:3 Then the LORD said, “My Spirit shall not abide in man forever, for he is flesh: his days shall be 120 years.”
When Adam sinned Adam subjected all of creation to futility and corruption Romans 8. There was now no possibility flesh in its fallen state to inherit externality. Man was not created eternal, he would become eternal, hence the tree of life in the garden.
So as a result of the fall and the mixing of genetics with the fallen sons of God, the life span of men diminished, at God’s decision. By what means? Certainly there are natural explanations but I don’t see the need to go into Biblical cosmology at this point.
I think the answer is clear, God reduced man’s lifespan because he was but flesh (corrupted/defiled) and decided to limit how long a man can live without His Spirit and therefore His guidance. Especially since even with God’s Spirit men (the daughter’s of men) still chose to sin against God and align themselves with the gods (sons of God or the elohim) against God. And learning from their elohim counterparts all manner of knowledge both useful and destructive. This was essentially gnosticism.
So man proved to chose against God even with the Spirit of God in him and so God limits the lifespan of man.