When you are predicting future behavior, you typically obtain data from the more distant past (e.g. say January to May of a certain year) and then observe behavior during an intermediate time (e.g. say July/August of that year) so that the model you fit can predict future behavior for new observations available in September or later that year for which the outcome is not known yet. Your training data must have the outcome variable you are trying to model so that requires the data to be old enough so that you already know the outcome. You can then collect other information that might be helpful in predicting that outcome to build your training data. Depending on the availability of data, the length of the window you are trying to predict into (e.g. one month ahead? two months ahead? etc...), and your business objectives, you might need to alter your time windows and which questions can be asked.
I hope this helps!
Doug
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