I uh, believe Drew said in another thread that the kid is actually his girlfriend's, but they plan for him to be his father. I don't think at 17 you can legally be the non-biological parent of a child, but legality isn't everything, and certainly means less to a kid than someone who's there for them and supports them.
Back to the original question, Drew, for a child that young, unless they're having an abnormally precocious puberty, hormone blockers probably wouldn't be warranted for at LEAST a couple more years. I developed earlier than almost anyone in my grade, and even I didn't have any noticeable changes until I had just turned 11.
If he is unfortunate enough to be showing signs of puberty already, even a family practice doctor would probably agree to administer hormone blockers without need for mention of the gender issues, it's just not fair or even healthy to begin puberty at 8. If you're thinking more for the future, your son would most likely need a therapist's help for obtaining them.
I'm not suggesting or insinuating that your son's declaration of being transgendered (or whatever descriptor he uses at that age) has anything to do with your influence, but you should know that if a child therapist/psychologist knew of your trans status, it's probable that they would scrutinize your son's motives more than they would a child with two cis-gendered parents.
Also, since I believe he is not your son by birth, it could be seen as more as a 'nurture' coincidence, than 'nature', if you get my meaning. I can completely believe your son felt this way regardless of and maybe be prior to your influence, but you have to remember that mental health professionals very often are looking to rule out 'environmental explanations', or other mental health issues. While it's true that getting on hormone blockers is typically easier than getting on hormone replacement, where children are concerned many in the medical community require a lot more observation and evaluation than they would with adults.
