Holden can be a "catcher" he can use his desire to preserve innocence by becoming a teacher who inspires students. He can encourage children to embrace their youthful imagination and really help kids enjoy being a kid. Have fun in life when you can, Holden can participate in this by being a great teacher!
There are plenty of adults who embrace a youthful exuberance, they are people who don't become too jaded in their view of life, they are hopeful. Holden can become this type of adult, he doesn't have to become a phony. He can be a grownup who tries hard to understand kids, since he feels like no one really understands him.
Holden has the potential to be a great teacher, to assist kids in their enjoyment of youth, to help them grow up without losing all of their youthful idealism. To still believe in things that only exist in the innocence of childhood. It is hard to capture and maintain this feeling in a cynical world.
Holden wants to be the "Catcher in the Rye" because he wants to enable children to stop growing up and having to face adult problems. However, Holden's dream is unrealistic. No one can really stop children from growing up or shield them completely from the problems associated with maturing. To do so would severely handicap the child because he or she would not be ready to deal with adult problems. Holden's dream is a result of his inability to deal with Allie's death and he doesn't want other to have to deal with death either. Unfortunately, we all must come to terms with adult realities at some times in our lives or we will not grow. Holden is stuck in a "holding" pattern and until he is able to face reality he will never be able to move on in his life.