"I haven't been able to figure out why creationists think ID supports a young earth interpretation."
Creationism...i.e a literal interp of the old testament, is a different version of "Intelligent Design." The two get mixed up frequently and this causes endless and meaningless exchanges between ID folk and Darwinists. Creationist ID is the straw man used by Darwinists to dismiss all ID.
I don't know what "all ID" is. Behe testified under oath that there is no research supporting such key elements as irreducible complexity. The Discovery Institute says ID has not established itself to to point where it should be taught in school.
Personally I think all of science should be taught as provisional. It was when I was a kid.
But that is not what the Dover school board wanted. They wanted something to discredit common descent (and they are on record as having this motive). But ID does not dispute common descent, so what's the point?