One approach:
sortrows() on the ID column, and the date column in descending order. unique() the ID column with 'stable' and take the second output. Use that to index the sortrows output to get just the first (newest because descending order) entry for each ID.
If necessary re-sort on the first column.
Or...
findgroups() on the ID, and splitapply() specifying a function that will receive the variable entries that are associated with a single ID. The function would datetime() and max() to get the index of the maximum and return that entry from the variables.
