As I have said, God didn't bring death or illness into the world.
God's gotten life right 100% of the time. However, the first humans misused their God-given free will and brought death and illness into the world.
Of course, if God hadn't given Adam and Eve free will, they could not have made such a bad choice.
Maybe they would have lived forever if they didn't have free will. Then again, life would be less enjoyable if we were essentially brainwashed into acting good.
My theory is that when Adam and Eve "ate the apple" they mutated their DNA. That could explain the longer lifespans of the earlier humans mentioned in the Bible.
Human DNA gradually became more corrupted in succeeding generations, leading to more frailty and earlier deaths.