I agree with it to some extent, but not completely. It may be, though, that your perspective will be different since you are a teenager and I am not.
To me, teen years are fun in that they are full of possibilities and not very full of responsibilities. Teens do not have to make a living. They do not have to care for children or worry about their careers. In a sense, they have more time and freedom for fun than adults do. Teens are also at a point in life where everything is ahead of them. They can still imagine that they will be anything they want to be. They have not had any serious dreams that they were unable to achieve.
However, they also do not have as much stability and security as adults do. They have to worry about whether they will be able to have a good job. They have to worry if they will find love and happiness in a marriage. This is more of a problem for teens than adults.
Therefore, the teen years are fun, but they are not without their problems.