Hehe I was 12 or 13 when I went meatless, and was living with my mom and bro at the time. My brother sure made fun of me, and my mom was initially totally against it, thinking I'd be "deficient in protein" and stuff. I ended up reading tons of stuff from the library about human nutrition, animal rights, vegetarianism, etc and quoting facts at her when she started up, but she also though I'd hardly last a week. I lasted way longer, as I went vegan at 18 and am turning 21 in July. At first it was difficult, and I kept having to remind myself that the yummy-looking stuff on that plate was some tortured animal's corpse and not food, but after a while the idea was as repulsive as killing a baby to eat her or chomping on my brother's arm.
Depending on the parents' usual recipes and budget, they can easily accomodate you. Offering to cook new veggie dishes from time to time is great, but it doesn't take much effort to leave the ground beef out of their spaghetti sauce or add TVP instead. Variety in your diet is good, of course, but don't feel like you have to rush into eating sprouts and tofu and tempeh and all that stuff right away if you're not used to it. (I actually just about never eat sprouts, don't cook, only eat tofu if it's pre-flavored or cooked by someone who can cook tofu well, and haven't really had tempeh much at all.)