Men transition very well at any age as a rule. You would obviously (unless blessed with a flat chest) need 'top Surgery' but other than that you have the 'luxury of waiting'.
If however, you are a younger adult or adolescent you would need to be very careful and MUST have a specialist consultant in this area. In the UK it is at the Tavistock see UNDER 18http://marketplace.transgenderzone.com/?page_id=79
This would be a 'puberty blocker' see - http://library.transgenderzone.com/?page_id=2794
Meaning puberty is put on hold to prevent breast growth in the first place. And the mental trauma of it!
It is a very complex issue and not to be taken lightly. Testosterone WILL
make irreversible changes to your body and you voice will break and sound masculine.PLEASE READ MY DISCLAIMER!