Doesn't matter if youre 14 or or 40 if you live under your parents roof it's only right to respect their rules. If they are against you using steroids, its probably because they're not educated on the subject and it's NO surprise they went through your mail. You can say federal offense and still not budge your parents. Some folks are just that way.
x 2 for PO box
Using a friends house is really not a great idea, because if for some reason you have a questionable item mailed to them, its their reponsibility if they break the law by recieving it and you're just putting them at risk. if theyre your friends and they still live with their parents too it'd be even worse then sending it to your house again.
my 2 cents