The Messenger of Allah (sal Allahu alaihi wa sallam) said: “Woe to him! Woe to him! Woe to him!” “Who is he, O Prophet of Allah?” the Sahabah enquired. He (sal Allahu alaihi wa sallam) said: “He who finds both or any one of his parents in old age and he does not enter Paradise (by serving them.)” [Muslim]
One of the routes to Paradise goes through serving one’s parents in their old age, when they are old and irritable and we are young and have lots of things to do. It is the reverse of when they were young and had lots of things to do but took care of us.