I don't know about the long term hormonal effects, but here is my take on the age debate...

If you're an athlete who has a chance to get a scholarship, play pro ball, etc. then I think you need to take it. I don't think it is healthy for teens to take it, but considering what is at stake I think it's a necessary risk. For all other reasons, I think you should be at least 25 and have 5 good years of training and diet under your belt. Again, these are just my opinions.