Hello stellar.
Welcome to the board.
I think Monika and Byrony make a lot of good points.
I'm a few years older than you (I'm 26). I think depending on your priorities and situation will affect how great some of the ramifications of pursuing NBE may be for you:
*Having your own children. Since being a teen, I never had an interest in having my own children, so this was never an issue for me. Why you may not be interested in having a family sometime soon, do you think your feelings may change on this matter, say in the next five or ten years? A question to ask yourself I think is "how would you feel if you learned you're permanently and irreversibly sterile?" Do you think you would feel happy, indifferent or sad?
*Paying for NBE herbs. Without knowing your financial situation I can't say how affordable NBE herbs will be for you. At your age, a lot of my income was going towards paying off college loans and saving up my money.
*How secure/confident you feel with your transgender feelings. Let's say you decide to pursue NBE. Six to twelve months later, your growth becomes noticeable. How do you think you would feel when other people notice and comment on your growth? What about when you go to the doctor and they have to listen to your heart or otherwise examine your chest? Would you feel mortified or hesitant to lift up your shirt? Or would it not be an issue for you? From a medical standpoint, bear in mind males having breast development is not the norm and not desirable for the majority of males. Unless you're upfront with your doctor, your doctor may assume you don't want to have feminine breasts and would rather have a flat masculine chest. I think the important point in all of this is by telling your doctor or anyone else that in the very least you're not bothered by your breast development, you're indirectly expressing your transgender identification. If you're curious, I suggest visiting a gynecomastia forum to see how males more frequently react to having breasts.
Here's a thread I started about being noticed:
http://www.breastnexus.com/showthread.php?tid=14325
For me I can get breast growth on as little as 2,000 mg of pm. Getting brain rewiring or the mental benefits of pm has been a bit tricker for me. I've had to adjust my doseage several times to maintain my brain rewiring. Also, as Monika mentioned, not everyone gets mental benefits from taking pm.
Pursuing NBE may be a very rewarding path for you, but I don't think it's a path that should be taken lightly, regardless of age.