Transfem

Yeah I've heard the claim that you should wait for at least a year to start progesterone, but honestly I think it's bullshit. As far as I've been able to tell, it's based on the fact that cis women don't start producing progesterone until a year or two into puberty, but hormonal transition in trans women is not really a one to one analog for female puberty. For one we aren't going through all of the other puberty changes because for those of us who have already gone through the male puberty those other processes are already complete, so trying to match the start times for the release of hormones in adult trans women to those of pubescent cis women is at best an ok starting guess. Beyond the comparison to cis female puberty there's really no evidence at all in support of starting earlier or later. It's also really hard to determine if the anecdotes about starting progesterone too early reduce breast growth because there are just so many factors including genetics, how much estrogen they're taking and by what route, how much progesterone they're taking and by what route, etc. Given the seeming default of the medical industry to constantly push trans women to slow down our transition, as well as the lack of evidence one way or the other as far as start times for progesterone, it seems more like harmful misinformation than well supported medical advice.

Given all that I would say go for it now. I started immediately but I took it orally for the first month and a half so it probably didn't really do anything for that. It's been a little more than 6 months now and my boobs seem to be growing very nicely. I've already got boobs that are bigger than some of the trans women I know who have been on hormones for 2 years or more. A lot of that probably comes down to genetics, but that's kind of the rub. There's no way to know for you specifically whether waiting is better or not. There is some evidence supporting that progesterone does increase breast growth in trans women, so on the one hand you have evidence saying progesterone makes our boobs bigger, and on the other you have people claiming without evidence that starting too early is detrimental to breast growth. These seem to be contradictory positions, but one has evidence to support it. It seems like a no brainer to me, but in the end it's your body, so do what you feel is best for you.