The next rank is a huuuuuge deal to a 9-year-old yellow belt in a suburban taekwondo school; it's not likely to be such an enormous thing to an adult.
While I think this is true for the majority of students I have experience with several students where the rest of their lives offers them nothing and progressing (gaining rank) in Aikido or whatever art they are in is the only think they have in their life. Their life is going to practice and ranking up as much and as quick as possible. So every rank is a huuuuge deal. Even to the 30-40 year olds.