I'm a metal guitarist, similar age, and also an vocalist, more or less.
I don't exactly know what to tell you, but you don't need to tell your parents if you don't want to. If you have a smartphone or tablet(I use a Kindle Fire), you can actually record on it using an application called Audio Evolution for Kindle, and there are various other digital audio workstations for different devices. Audio Evolution costs money(I think it's 7 dollars), and most good DAWs cost some money. You could go the easier rout and use a tape recorder, but you may have to ask your parents to buy one. I would actually recommend the tape recorder over digital because it's more reliable, and portable device microphones sound like crap. A computer, if you have your own would be very helpful for recording, too.
I think it would be best to tell your parents, though, an they could get you better equipment.
Sorry, I just realized I was quite late to reply.(edit)