I wasn't being sarcastic, or mocking anyone's beliefs, scientific or religious. Nor am I an atheist or got lost and think I'm on Slashdot. I was merely putting forth a question I've always thought was intellectually interesting, something that's supposed to be encouraged here. [1]
In that case, the answer to your question is that there is no answer, that there can never be an answer (unless God tells us) and that there does not need to be an answer.
If God really made it so that it's impossible to tell that they are not 4.7 billion years old, then it is simply impossible to tell so, hence there can be no answer.
And there does not need to be an answer, because if there really is no way to tell that they are not 4.7 billion years old, then by definition there cannot be any situation where it would make a difference. So, it's perfectly valid to just state that they are 4.7 billion years old.
I am in fact atheist, this is the viewpoint that I have from the discussion whether maybe our entire universe is just a computer simulation ran by some alien race or such.
If we talk about it with the religious tangent, there's of course further questions: Some people interpret the Bible to contain an age of the universe. So, is that interpretation of the Bible wrong or not? And if it's not, why would God want to trick us with those rocks? Did he create the universe some few thousand years ago, but thought it'd be a more interesting world, if there was some backstory to it? So, does he want us to explore this backstory? Or is it a test of your faith in the Bible? ...which to my knowledge really doesn't state a concrete date for creation, so at least to me that'd be strange.
[1] https://news.ycombinator.com/newsfaq.html