It depends upon which creationist (especially the young earth variety) whom you ask. Many creationists tend to be hostile to relativity theories, but now some are trying to use SR and GR to support their young earth creationism with the space/time entity concept. Fossil placement has also been used to try to support the great flood. They generally attack carbon dating methods, even though many creationists seemed to have little problem using this method when it may had potentially supported one of their arguments.
Irreducible complexity has also been used by them, and may be their strongest argument thus far, due to the difficulty that certain bacteria may have had evolving and surviving because of the structure of their bodies. Their contention that the bacteria involved here would had never evolved in such a way because that would have been detrimental to their survival, shows that natural selection failed here. The other stronger argument here is the complexity of DNA coding. Of course young earth creationists aren’t the only theists to use these arguments, and neither of the latter two subjects that I’ve brought up deal with the age of the universe.
True science must not be about proving propaganda, but about finding the truth, whether we are comfortable with what that is or not.