> It's not impossible from a scientific perspective ... to create a simulation with intelligent life in it and to save some resources by starting 6000 years ago from a complex seed state rather than simulating 16 billion years of physics to see the intelligent life emerge or not.

I'm fairly certain simulating 16 billion years of physics (or 6000) in a shorter timeframe than 16 billion years (or 6000) is, in fact, scientifically impossible. Mathematically impossible, even, because it leads to absurd consequences such as the simulator being able to simulate itself faster than itself.

In our own universe — sure. In some "bigger" universe it could be entirely possible, ours would fit nicely.

You wouldn't need to simulate much. If you were a simulation, you could exist right now only, and merely have false memories about everything else.