If Adam and Eve were the first people on earth, how did cavemen exist? I'm a Christian and don't know how to answer people when they ask me that.
People have a strong tendency to assume that each prior generation lived more primitively than the current generation. It is true that our technology increased, but the assumption that men once lived in caves is exactly that -- an assumption.
From the Bible, we learn that men very quickly built towns (Genesis 4:17) and some chose a nomad life living in tents (Genesis 4:20). They had musical instruments (Genesis 4:21). They were able to forge bronze and iron (Genesis 4:22). This is not the primitive society that is typically claimed.
That is not to say that some people over the years did not choose to live primitively. We know that native Americans used caves for hunting expeditions, so it would not be surprising to learn that other cultures did the same in the past, which would explain the drawings of various hunts on the walls of caverns. But there is a difference between temporary and permanent shelters and a difference between typical and emergency shelters. For example, Lot and his daughters lived in a cave for a while (Genesis 19:30), but they had been living in a large city prior to that. During a time of war, many in Israel live in caves (Judges 6:2; I Samuel 13:6).
The problem is that people find evidence of primitive living and assume that this evidence must be older than living in buildings. Yet, there are people in American today who voluntarily leave their homes to live primitively for a week or two and we call it camping -- a form of recreation. What is missing is evidence of pervasiveness and gradual development.