Where did the universe come from? Atheistic origin science has no answer.

[Tonus]

an unassailable fact : universe is 13 billion years old.

I don't know if it's unassailable, but consensus is that the universe is around 13.7 billion years old. And it may have sprung from the carcass of the previous universe, or may be one of many that sprung from an existing universe, and so on. The point being, we can see that it is here and physicists can speculate on the possibilities for its previous and/or ongoing existence using science and mathematics.

"whom you claim cannot be observed". that part is correct. for instance, an entity standing right in front of you claiming to be God wouldn't be proof.

Right, so you understand the problem: you posit the existence of an entity who isn't standing in front of me, or even anywhere in the universe, and does not --since it cannot-- make any claims or even leave a verifiable trace. And he is mysterious and inscrutable but you know him so well that you can continue to define and redefine his attributes whenever reality threatens to pull back the curtain. But you think the other hypotheses are the poorer ones for explaining the existence of the universe.