<p>If you stay in Philippines for 4 years, you’ll loose your green card. You know better, if it’s to your advantage to explain this to your parents, but that’s US immigration law. </p>
<p>You can apply for US citizenship on your own the day you turn 18. No parental approval required, but USCIS will keep sending their official mail to your home address. It’ll take 3-6 months to actually get citizenship. Your application will be processed fast because of your young age. There’s a rather big application fee, but I’d suggest you send a letter with your application, explaining how much you want to become a citizen, study in US, see your bright future as an American, and ask for a waiver. You should be proficient in essay writing by that time, right? 
Writer’s pay for this particular one is $675, as of today.
[USCIS</a> - Application for Naturalization](<a href=“http://www.uscis.gov/portal/site/uscis/menuitem.5af9bb95919f35e66f614176543f6d1a/?vgnextoid=480ccac09aa5d010VgnVCM10000048f3d6a1RCRD&vgnextchannel=db029c7755cb9010VgnVCM10000045f3d6a1RCRD]USCIS”>http://www.uscis.gov/portal/site/uscis/menuitem.5af9bb95919f35e66f614176543f6d1a/?vgnextoid=480ccac09aa5d010VgnVCM10000048f3d6a1RCRD&vgnextchannel=db029c7755cb9010VgnVCM10000045f3d6a1RCRD)</p>