If he were to apply for paternity, does that mean that he would be liable for the child support arrears since Xander's birth or do payments start after he legally becomes the father?
Yes. Once you do acknowledge paternity, and it's actually accepted (the mother does not contest it and contest it successfully), your rights to custody and visitation become a live issue, and child support is as well,
nunc pro tunc, which is Latin for fuck you, I know Latin, but in normal human language, retroactively to the effective date. In other words, the failure to do it to that date is considered a clerical error rather than a substantive one.
In addition, either parent has the right to sue over this issue. So the mother could sue a father refusing to acknowledge parentage, or oppose the claim of paternity. In either event, the issue would be resolved by a DNA test, or the failure or refusal to take one. It's a little procedurally complex, and the burden of who has to prove what depends on the case. So you could either be in a situation where you'd have to take a DNA test to prove you were the father, if you were the one trying to prove that, or the actual opposite, where you'd have to take a DNA test to prove you weren't, and then there would be the issue of whether it were even possible to test the child.
I don't know how they do it in California, probably some fucked up retarded way, but forcing even a cheek swab DNA test on a child is possibly also tricky.
I am fairly sure about one thing, though. The Gunt will never prove his paternity judicially. He will never do anything that will put him on the hook for child support. He is a subhuman. He will never be a father. Even his own father, who very well may have fucked him up the ass, was a better father than he is.
I'm deadly serious, people like Ralph are a blight on the world for the misery and pain they spread. With the only commiseration that they're fun to gawk at.
Ethan Ralph is a walking example of the degeneracy of Western civilization and why a judgment from God on our sick society is coming.