I think it is still relevant yes, mostly because of the insight into the ever present generation gap and the reveal of society as full of phonies/phoniness/hypocrisy. Apart from that it is still excellent as pure litterature.

Here in Denmark I read it in both Danish and English high school freshman year. (Obviously it was something the respective teachers had worked out at the start of the year... - I think they figured that our essays would be better if they joined forces.) This was back in 1983. My school started english in 5th grade so we had had 5 years of english education I think... Of course it helped that we read both versions at the same time.

As for "coming of age" - hmmm - I am not sure if "coming of age" is the central theme of the book - "coming of age" in my understanding of the concept has always been centered on the sexual awakening, which is not crucial to "Catcher" - Holden is past that point and is more concerned with existential questions like "meaning of life"/happiness/"religion"/work/study and such...

My 2 cents ;-)