If the sticky has not been edited or changed, the amount suggested there is ridiculously high. REAL gyno will shrink (but will NOT disappear completely) if you will just drive E2 low enough and keep it there long enough. This does NOT NOT NOT mean that you have to eliminate every trace of estrogen from your system. That's ridiculous and possibly even dangerous for a number of reasons.
Keeping the above in mind, it is possible to shrink REAL gyno with more typically used AI's like arimidex or aromasin. The reason letrozole is typically used is because it is extremely powerful and therefore quick and effective. However, it is also usually total overkill. Off the top of my head, expect all over aching as your joints dry out, possible injury stemming from the latter, complete, utter loss of libido, a general ugly, dead, soulless feeling. Trust me, I have warned probably a hundred guys about this and they never listen and they always tell me I was right afterward.
Maybe you'll be the first.
The main problem, though, is that most guys don't have gyno in the first place.
In the very off chance that you do indeed have the real thing, about .625mg letrozole a day, later titrated down as your libido starts to tank and your joints start hurting. About 2 weeks should see significant reduction in size.
Again, though, for most pubertal gyno, if it is for real and seriously bothering you, surgery is probably a better option.
You know what cured me of worrying about my gyno? First, actually getting it and realizing what I'd had up to then was NOT gyno. Then, getting big enough that it is no longer noticeable. Finally, keeping my estrogen at a manageable level all the time prevents it ever getting any bigger than it currently is. I haven't worried about it, to be honest, in a looooooong time.