SQL & PL/SQL :: Write A SELECT Statement That Returns One Row For Each Customer With Four Columns

I am student of Oracle programming(SQL).Has a question on MIN and MAX functions:

- "Write a SELECT statement that returns one row for each customer with four columns--the customer's first and last name, the date of the customer's most recent order, and the date of the customer's oldest order and the difference between the two dates. Sort the result set so the customers who have been ordering with the company the longest appear first. Use most recent order date as a tie-breaker for the sort."

where orders and order_details,customers are 3 different.this is my query ...but its not working.

SELECT DISTINCT customers.customer_first_name||' '||customers.customer_last_name AS Customer_name,MAX(order_date) AS "Most recent order", MIN(order_date) AS "Oldest order"
FROM customers
INNER JOIN orders
ON customers.customer_id=orders.customer_id
LEFT JOIN order_details
ON orders.order_id=order_details.order_id
LEFT JOIN items
ON order_details.item_id=items.item_id
ORDER BY Customer_name