because it was quite clear in the Torah... it did start with Adam.
It depends on which parts of the Tora you pick and choose for literal reading.
You have obviously decided that Genesis is literal and that descriptions like "the hand of G-d" are not.
Judaism disagrees with that reading. The Talmud mentions that there were over 900 generations before Adam.
It is perhaps ironic that a message like that is "quite clear" to you but less clear to those who the message was for, who can read the language and understand it, and who still live according to that worldview (and have never been told that the old law doesn't apply any more).
My approach to any statement of the Bible is this:
1. Read it literally
2. If it directly contradicts evidence I have seen, try a different literal reading, taking into account historical context.
3. If that also contradicts evidence I have seen, assume it's not literal.
4. Figure out the symbolism.
"In the beginning created G-d the heavens and the earth."
Step 1: Done.
Step 2: I have no evidence that G-d didn't create this world and can safely assume that "the heaves and the earth" refers to this world.
"Noah was 600 year old."
Step 1: Done.
Step 2: I know from biology classes that no man can be that old. There are sound reasons for why the brain would stop working long before that age. Hence I go for a different literal reading. I know that the word translated as "year" is "shana" and I know that "shana" comes from the root WNT (W is /sh/) which means "change", "alter", "repeat". I also know that the legend is originally Sumerian and that Sumerians measured time differently. Plus "shana" has a basic meaning, derived from the root, which is "unit of time". Hence I try a literal reading with "shana" translated as a Sumerian unit of time (like a month). Suddenly Abraham is 50 years old and the statement doesn't contradict the evidence any more.
"The hand of G-d did [whatever]"
Step 1: Done.
Step 2: Cannot see a hand of G-d anywhere and the laws of physics I know would not allow for such a beast to exist.
Step 3: Statement is probably symbolic for something.
Step 4: I assume it means that [whatever] happened as if guided by G-d and was probably beneficial or should be understood as if it ultimately will be.
I don't know your algorithm for which parts to read literally, but I have found that the result surprise me. You read passages on angels literally but not passages about G-d. And you see symbolism for Jesus in everything, even if it literally just described mundame (and completely possible) situation in someone's life.
Perhaps you and I start with a different assumption of what the result be?
You seem to want the result to a) confirm that Jesus is a messiah,
keep the world simple and in a state where a literal reading of Genesis puts you on par or above a smart biologist or physicist in understanding the universe, and c) find explanations for natural phenomena that don't require you to study physics or chemistry.
I want the result to a) allow for the greatest possible creation,
be compatible with all findings of science, and c) fit nicely into a system of Semitic legends and a world where lots of different cultures can live together without one of them being "wrong" about something important.
A god who is a bad designer or vile enough to create diseases, 1000-year old men, a universe younger than many things in it, and a philosophy that believes that everybody else is wrong and that their findings must be replaced just doesn't fit into my view of G-d and His world.
I CANNOT accuse G-d of having created such a world. It's not my place.
And if Christianity would require me to do that, it's difficult to accept its founder as the messiah; especially considering that his appeance did not foreshadow a glorious time for Israel but the destruction of Israel and the dispersal of the Jews to everywhere in the world for 2000 years.