"Radiocarbon (C-14) dating (and applicable to all methods of dating)"
This can't be used against "aged creation" because the idea is the universe was poofed into place exactly *as if* it was X years old. There is no way to test that simply because there's no way to distgiush an old universe with a "fake old" young universe.
"Not to mention that it's assumed to have always been present in the same concentration."
Correct. It's formed and lost, and currently that is at a balance. It would always -end up- at equilbrium, but we don't know if the point of balance has changed. OTOH, C-14 dating is only used for fairly recent dating, and there are other methods.
"Isn't the retention of acquired characteristics Lamarckism? And doesn't this assume that mutation results in improvements?"
No, and not exactly. Lamarckism applies to physical characteritics, genetics to the genes of the organism. The difference is that Lamarckism predicts that if you lost an arm, then have children, your children would -also- not have that arm. It also predicts little or no variation in the children, since anything not expressed doesn't exist and can't be transmitted. Neither are true.
Mutations don't always result in improvements; actually most of them are probably BAD for the organism in question. Random chance though, so you'll likely get a good mutation eventually. My biology teacher put it in a good way, like so:
"Say I take a 100-sided dice, and bet you $5 that I will roll a 1. If I roll anything else, I loose. Good bet, right? Now, is it still a good bet if I get to roll the dice *1000 times*, and if I get just one 1 in those rolls I win?"
The best example of this is antibiotic resistant bacteria. They normally don't compete any better against the rest of the bacteria, so their numbers are fairly small. But the antibiotic comes in, kills off the rest of the bacteria, and their numbers can explode. Instant evolution.
"But anyone who says that science "proves" evolution is misinformed about the basic unproven assumptions vital to evolution."
Also known as "the current best guess."
Phoenix-D