Total BS...
There are better ways to exercise your brain that will be many more times better than Calculus. This is HW so one that comes to mind is programming. But there are so many more. Here are a few, understanding and fixing a car, understanding music and playing music, art appreciation, literature and understanding the human condition and on and on. Recent research has shown that doing daily exercise is a great way to keep a healthy body and brain, rather than sitting on your butt learning a useless subject.
Yes, there are professions where Calculus is needed and there are people that truly enjoy math. Cool, take all the math you need and want to learn. You should take it.
Anyone that tells you that Calculus is a good way to exercise your brain is just trying to justify their job. Don't for a minute believe that it's the best way to use a limited resource like your time.
Source: Me, it took me 3 semesters of Calculus to figure out that it was useless to me and 90+% of the people that take any of it.
P.S. note: Many people disagree. Good, you should not take it as absolute truth. I guess my real point is that you should question whether you really need to take Calculus. Don't just take it blindly because you are told you should. You have other options.