Not to get all "churchy" on ya, but this is a great Biblical perspective as to why eating animals and fish is A-OK with God. :)
The New Testament records that Jesus did eat the Passover feast, which would include the eating of the roasted lamb (Luke 22:14-15). In fact, before the last Passover meal, Jesus specifically instructs his disciples to prepare the meal, including the lamb, for their observance.
Then came the first day of Unleavened Bread on which the Passover lamb had to be sacrificed. 8And Jesus sent Peter and John, saying, "Go and prepare the Passover for us, so that we may eat it." (Luke 22:7-8)
Not only did Jesus eat lamb, but he also ate fish (Matthew 15:34-37). Jesus also promoted the catching of fish for the purpose of consuming them.
So Jesus said* to them, "Children, you do not have any fish, do you?" They answered Him, "No." 6And He said to them, "Cast the net on the right-hand side of the boat and you will find a catch." So they cast, and then they were not able to haul it in because of the great number of fish...So when they got out on the land, they saw* a charcoal fire already laid and fish placed on it, and bread. 10Jesus said* to them, "Bring some of the fish which you have now caught." 11Simon Peter went up and drew the net to land, full of large fish, a hundred and fifty-three; and although there were so many, the net was not torn. 12Jesus said* to them, "Come and have breakfast." None of the disciples ventured to question Him, "Who are You?" knowing that it was the Lord. 13Jesus came* and took* the bread and gave* it to them, and the fish likewise. (John 21:5-6, 9-14)
http://www.lavistachurchofchrist.org/LVarticles/DidJesusEatMeat.htm
The Old Testament is full of instructions on which animals to eat.
And there's no instruction to wait until they die of old age.