By checking the statevariable: "CompressiveYieldingStress", we saw that the value was -1.
If in the input file, we use LDPM-X for the material properties, then the change of the STV name (CompressiveYieldingStress) in mRCConcreteXUD does not matter because only mRCConcreteX is read. That explains that why the aging module cannot find the state variable index according to the name you modified in mtRCConcreteXUD class.
If we use LDPM-XUD (the userdefined version), at the moment where I use LdpmModules in my input file (where I use the Aging part), LdpmModules is not reading mRCConcreteXUD but mRCConcreteX. The issue is maybe because LdpmModules cannot recognize the UD version of the material model.