I would like to comment on this subject because I have first hand knowledge of male pattern baldness and HRT's effect on it.
I'm young (19), yet I have male pattern baldness. I started HRT 3 months, 11 days ago. After a while, I noticed my hairline seemed to have baby hairs. They'd grow and new ones would grow underneath. I'm not sure how much growth to expect, but I just want to say that depending on certain factors, your balding might slow, stop, or even begin to reverse itself. I cannot predict the future, though. My old hairline may never fully grow back, but some progress is better than none.