Trips with riders born before the year 1927  were removed.  I believe these birth years were incorrect since most 90 year old are relatively frail and would use other methods for transportation that a bike share.    Also all rides without a birth year were removed rather than provided with average age to avoid classifying them all as younger riders.
    Outlier rides with a trip duration above 3 hours were also removed.  These rides likely were recorded as being very long due to an incorrectly docked bike since it is quite expensive to rent a bike for that much time and it is doubtful many people would do it intentionally.