Hi Coat, 18-1/2 is not too old, take me for instance I'm 57 and started transitioning last year, the results are really good so far although probably slower than what you would will get. I looked at your picture and you really will look great after hormones get going.
To get started you need to find a gender therapist, if you are under your parents insurance you will need to tell them, this is one of the hardest things you will do. If they are pretty open to things in general and if you have a good relationship with them it may go ok, if not be prepared to be disowned or kicked out, there is no way of really knowing. There are allot of resources here on coming out to your parents, so read and then decide on what you want to say and either write the words down on paper or in a word document, keep it short only a page long, you don't want to give information overload, find a time where there are no other crisis going on and they have time, maybe schedule a time, but do it in person. I'm not trying to scare you but these are the sad realities sometimes. Get and read the book True Selves this book explains things in detail and was written by a gender therapist, give it to your parent's to read.
You need to start growing your hair, it takes a long time to grow to the length you may want, hair grows about 1/2" a month.
Get some girls jeans, they look similar to guys but can be a little fancier if you want, girls tennis shoes are the same way.
Keep us updated on how it's going.
HUGS!
Paula.
