Hopw would you scientifically prove the age of a creationist's universe?

Creationists believe God created the universe. If they’re Judeo-Christian and cite the Bible, they estimate that it happened approximately 6,000 years ago.

If you follow my postulations (1, 2, 3), then it’s arguable that the universe might have been called into existence fully formed. Meaning, for example, light from a star 2,000,000 light years away is already laid down such that that star is visible in the Earth’s night sky. Or that carbon material in the Earth’s crust was placed as coal, oil, diamonds, etc.

How does one scientifically dis-/prove such thinking? What tests could be performed that are external to the system in order to get a non-biased result?

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I’m curious because I see a lot of criticism of creationism based on scientific evidence of the age of things. But without allowance for what seems to me to be obvious limitations of science itself. I’m not all that smart, so I’m wondering if anyone else has figured it out yet.

For the record, I don’t think creationism should be taught in science class at schools. It’s not science.

Yes, I realize that by the creationists’ line of reasoning, what’s to say we weren’t cooked up just 5 minutes ago with fully scripted memories of the past?