If someone is investigating differences in means between 2 groups, does it matter which we consider to be the IV and the DV? For example, can I use a t test to examine the difference in the age of children who have attained a certain developmental milestone and those who have not? Imagine the IV is milestone (Yes/no) and the DV age (mean). But clearly, the milestone does not cause the age. Is it reasonable to use a t test in this manner? Does presumption of causality matter?
And secondly, is it reasonable to switch round IVs and DVs in order to look at the data in different ways? E.g. to run some t tests with group (e.g. milestone) as the IV, and then run a logistic regression with all the continuous predictor variables (with group as the DV)?
Is there a better way to approach such analyses?