I am not an author, but I do read lots of stories on Nifty and other sites when I hear of them. If I like a story, I always send a comment to the author, no matter what his or her age (if, indeed, you can tell an author's age by the writing style). I don't always get an acknowledgement from that author, and that does bother me. Also, I enjoy email pen-pal relationships and encourage them without regard to age.
Clearly, I am intelligent enough not to make any comment or suggestion that would cause a government entity to put me under arrest for an inappropriate contact with a minor.
Given the opinions already expressed in this subject, I would like to add my two cents on the side of responding to anyone that sends you comments about your story. If nothing else, it is the courteous thing to do.
I also agree that there are an inordinate number of gay teen suicides and if there is any opportunity for anyone to possibly thwart an attempt by keeping in touch with someone that writes to you, go for it - it may save a life.
Until next time, PK