I don't know what the proper definition of "developmentally inappropriate" is in the specific or general case, but in practice, what is going to happen is that if the standards/tests are "developmentally inappropriate," you can tell because the scores won't go up no matter what you do instructionally. That's the functional definition, as far as I'm concerned.
For example, the number of times the average 3rd grader can bench press 300 pounds is zero. After a rigorous training program, it is still zero. Thus, it is a "developmentally inappropriate" assessment.