When can I start the Green to Gold Program?

You can apply for Gree to gold if you qualify or you have to get out and attend a college with ROTC.

Battalion/Brigade Commanders can sign off on Green to Gold packets, but it seems that their numbers are limited. Make sure that you set yourself ahead the rest of the unit, so you have the best chance. Speak with your chain of command and ask to speak with the BN Commander. Let him/her know that you are interested and ask for his/her guidance on what you need to do in order to get their approval.

You might want to google that. I think it is after you get out but I am not sure.