Coming out as trans can be quite tricky. When someone comes out as gay, people generally expect that "aspect" applies from that point on - the person will start dating and be seen to be in relationships with someone of the same sex. But if that person came out as gay and kept dating people of the opposite sex most of the people they cam out to would be a bit "WTF? Didn't they say they were gay? Are they bi?" A lot of trans people come out as trans months even years before they transition and it can be quite confusing for many people not familiar with trans or gender issues - "You said you identify as a woman not a man and yet you're still dressing like a man, etc - does that mean you're not doing it now?" Or, the other thing that can happen is that they see the fact "you haven't done it yet" as a sign of doubt and an opportunity to talk you out of it.
Anyway, my point is that it is perfectly fine to come out to people at any point you want to. Depending on where you are in the transition process though you need to also temper their expectations, understanding of where you are in the process and be prepared for push back and incredulity (if not straight away then in the weeks, months to come).
During my first attempt at transition I told my mother many months before I even expected to transition. Ditto my friends. My mother responded with stress and denial, especially as the months dragged on (no pun intended!!). My friends, I think, humoured me but just didn't take me seriously... I went out with them, from time to time as "Julie" but often as not they would also see me in guy mode. In the meantime all sorts of bizarre rumours about me were being spread. With my transition this time I told the majority of people - family, friends, colleagues - a week before I went full time. It sure was a lot less stressful not having to deal with confused, dubious or antagonistic people. My parents took it on board, they didn't like it but once they realised this was a real and full time thing they just had to go along with it. Things are good with my mother, not so much my father.
So anyway, coming out to your folks - if you do, be clear about what being trans means for you - even if you don't know whether you will transition or not in the foreseeable future. Be prepared for questions and denial. Chances are they will think you're telling them you are gay and other misconceptions. I found that, rather than trying to explain the "science of it all" (as if there's a clear answer there anyway), I mostly stuck to talking about my feelings and what I was doing to redress my depression and dysphoria. If you would like something from them - understanding, acceptance, help, etc - be sure to ask for it. You may get it, you might not, but you need to ask.
