Transfem

Starting around 6 mo would be ideal, but there's never a too late.

most people ive talked to started prog at like 6 months to a year, just anecdotal tho. i plan on starting at 6 months

I think over a year is probably fine. I started at 8 months and don't regret it, my boobs seem to be continuing to grow. There are people who report starting progesterone from day one and have normal breast growth.

You might already know this, but every time progesterone comes up I like to gently remind people that progesterone should be administered rectally to be effective, oral progesterone is filtered almost entirely by the liver.

It might be fine for cis women who produce endogenous progesterone and the less than 10% of the oral dose that actually reaches their blood is still helpful, but for transfem individuals, that won't meaningfully raise your blood progesterone levels to anything close to cis female levels.

At the advice of my doctor, I started progesterone at a little over 1 year of HRT, and I'm currently at 1.5 years, and in my mid 30s. They told me that the evidence of its effects are anecdotal at this point, which is why you get such unclear guidance for now. Progesterone in trans women hasn"t been nearly as well studied as estrogen at this point.

9 months to a year of E as a minimum is the advice I've encountered. 1.5 years is enough. I think cis women start producing it about 2 years after estrogen. You can start now or wait either is fine.

If you're worried about stunting breast growth, I have to ask, are your breasts currently growing? Mine seemed to have stopped growing at 6-9 months, and have been the same size since. Since starting progesterone they've gotten a bit rounder I guess, but still about the same size overall.

I've heard progesterone helps the mood of some, and causes depression in others. But for me, I don't know. It doesn't feel like anything. The changes, if they exist, are small or subtle. Maybe I'm taking the pills wrong.

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.