Question: So if Adam wasn’t the first person to live and die, did God create men sinful because men only die because they sin? And if there were men before Adam they must have been sinful because they died.
Answer: Adam was told that the day he ate from the tree of the knowledge of good and evil would be the day he would die, (Gen 2:17), but he didn’t die on that day, so God must have been talking about some other kind of death. Jesus said, "Whoever lives and believes in me shall never die" (John 11:26), but we still die a physical death so Jesus must have been talking about some other kind of life. That is the message of the Bible - humans, who are made in God’s image, can partake of the life of God if they choose to do so.
“They are darkened in their understanding and separated from the life of God because of the ignorance that is in them due to the hardening of their hearts” (Eph 4:18).
God didn't create us sinful, but he did create us with freewill. And freewill is exactly what it says: Free to do wrong as well as right.
When God first started to create life on earth, the ‘life’ started small. We have many fossils from those early days, and if we have fossils then it must mean the creature died. As ‘life’ got bigger we have fossils for the larger life too, and if we have fossils then it means those creatures died too. God gives and God takes away. That’s the rule; a rule that applies to humans too. However, each human has an opportunity to grasp eternal life.
This universe was never meant to last forever; it is slowly running down as entropy takes its toll. The Apostle Paul said, "Flesh and blood cannot inherit the kingdom of God". It seems that humans were never meant to live in this universe forever. Even Adam was not going to live forever, he needed to eat from the tree of life to do that.