Sometimes, age of a monument can be considered as a variable while considering many at a time. However, when considering only one monument, it has a fixed value. For such calculation, how to use fixed value variable in SPSS AMOs?
Inferential statistics, and SEM by extension, is about finding differences or relationships. If A is high then B is also likely to be high, and so on. You need to have variation in the data in order to see how they change in different circumstances. If you have one object at one moment in time then there is no variation in the object and no variation in time - it's not applicable to the analysis. And your conclusions apply only to that object at that moment.