From mostly hearsay that I seen and my recomandtion is when you reach tanner stage 3 and been on it at least a year.

There is not enugh research for any conclusions. Some started immediately and devolope round breast. Other cone shape. Now some develop cone shape even doing tanner stage 3 and a year part so that is even less fact.

Again there is not enugh research but I feel it is bad to gamble. Unless you find a certain feature from progesterone that you feel this important now. Why not wait? You will have tons of bennificts from estrogen and effects from estrogen that is good that you can only point to estrogen instead having to figure out if it either progrestrone or estrogen causing them.

Especially with the very minuscule risk of backdoor dht with progesterone.