Hi Lizabelle

It's really difficult when your family is that unsupportive. Mine was too. Be ready for difficult times, times where your folks will be pushing for you to live as a man and likely may try to sabotage your transition. My family was this way, but in the end they accepted and now I'm having SRS, due to their help. Do not lose hope! If they are open to dialogue, you may want try to talk about your feelings but it doesn't sound like this is your situation. You will have to prove them that you're capable of doing this alone, this is way the only my family accept. It may or may not work, but you'll never know if you don't try.
As for age, 18 is an awesome age, assuming that masculinization hasn't taken its toll. I started HRT at 18 and pass perfectly now. There's no situations in my daily life where I'm taken as anything other than a young woman. But presenting as a woman can be expensive. You will need to save. I don't know what point you are in education. If you can, do enrol in college or delay it 1 year max and get a job. Save, save, SAVE. If beard is a problem, wasn't for me but it depends, get that removed ASAP, with either electrolysis or laser hair removal. You will need money for clothes, HRT, hair, consultations, blood work, etc. I funded my transition by working in call centers and a child group home. You will have to be strong. It's likely you'll go through the early stages alone because of your family's unsupportiveness. I certainly did. Hope that's not the case for you but be ready for the possibility.
All the best,