If he created a universe that was much younger than it appeared, he might have done it for a reason other than tricking us. And I have no problem with the Lord tricking me, if it's done for my own good. I don't equate that with lying.
In that case I would just stick to probability and simplicity - looks old -> is old until proven otherwise.
Because we could say that nothing we actually see is truth for some reason... so in the end we could say nothing about anything real.
I can see your point, its surely possible. But in that case we have no certainity in anything, if God "masked" things to look what they are not, if you understand me.