Creating a Custom Property to Track Latest Trial End Dates

Is there a way to create a custom property that is max of a property value. Our scenario - we track user trial with a Trial event that captures trial_start and trial_end. if user requests trial extension, a new Trial event is fired with new trial_end date. We want to know how many users trial expired "before last x days", and for this we need to check the trial_end on the latest Trial event.