I don’t think the young earth argument is reasonable, but I also think people are being rude to those who make arguments on its behalf.
The argument against a young earth that is easiest for me to understand (and therefore explain) is stellar parallax. The best current measurement of star distances can find stars out to about 1600 light years distance. This only proves the universe is at least 1600 years old.
Fortunately about 6 weeks ago a new satellite was launched that should be able to measure parallax distances up to the 10s of thousands of light years. If this mission is successful then we would know that we are seeing light that left its star more than 6000 years ago.
At that point the remaining argument would be that the mission scientists are untruthful about what they report or that God created the universe with light already partly on its way to us.
Of course many other self consistent observations in astronomy already indicate tremendously older stars, but those self consistent observations are beyond something I completely understand.
” The best current measurement of star distances can find stars out to about 1600 light years distance.”
Um, where did you get that? Hubble has been looking at stars way past 1600 light years out.