honestly... try not to store it.

You need to examine why you actually need the data, and if you can't think of a good reason (except it might be valuable in the future), then don't store it.
If you do need it for analysis, machine learning apps, etc, try to anonymize it as early as possible, and not to keep raw data longer than you need it. (say raw data for 3 months, then just store aggregate info).

also.. for behavior.. you don't need years of information, studies have shown people change, so make sure the things people do recently are more important, and the old stuff gradually decays.