You can use the sort-key and apply the ScanIndexForward parameter in a query to sort in either ascending or descending order. Here I limit items returned to 1.
If you are using Boto2 and you have the sort key on one of the columns in your table, you can sort what you retrieve in order or in reverse order by saying:
result = users.query_2(
account_type__eq='standard_user',
reverse=True)