The Bollywood legend has taken on a cameo as a villain in the forthcoming remake of Agneepath.
Ranbir told DNA India: "I am hearing such amazing stuff about my father's performance in Agneepath. He is a brilliant actor.
"If a person is a good actor then the person will continue to work lifelong and keep giving good performances. He is 55 plus but he is still getting so much work to do.
"There is some sort of childishness [in him] when he gets offers for any movie or any new character. His passion for work... for cinema inspires me to do better work."
Ranbir added that he has no immediate plans to work with his father on a film.
"No-one has really offered us a script that both of us liked. We both are individual actors and if a good script, good characters come our way and and we both like it then we will definitely work together," he said.
In 2010, Rishi Kapoor criticised his then 28-year-old son for failing to establish himself in Bollywood.
The father and son will make their on-screen debut together in a Pepsi commercial, it was reported in September.