若者にありがちな悩みといえばそれまでだが、大人にとっては重大な問題だった。
The context is that the main character has never felt challenged until this point in his life. My guess is that the sentence means something like "although this is a common issue for young people (and that's the end of it), it's a big problem for an adult."
What does といえばそれまでだ mean in this sentence?
