Back in the prime of the boards, we had a 35-year old, a bunch of college students, several high school students, and some even younger people starting to dabble in composition. So the point is, the composers don't need to be "young"; it's just that we're not looking for a community of a bunch of professional composers that are all stuck in their ways and already educated and know how they are going to compose.
"Young" implies exploration, implies still developing and open to comments; it implies that you're still open to new musical philosophical viewpoints and that you're still trying to figure everything out for yourself. And if you're 78 years old and this applies to you, then Young Composers is where you want to be.