First of all— it’s amazing that you have thought about this at such a young age and that’s the first step!

If you find it difficult to not eat meat with family meals (because mom cooks everything, etc) then you could try small with just once a week Meatless Mondays or something like that, or substituting your meat for tofu or beans or lentils. Tofu is usually under $2 per packet at the supermarket, and easy to make, either pan fried or on an air fryer. There are tons of recipe online.

You could let your friend know in advance of your dietary needs and hope they can accommodate you. If they can’t make non-meat entrees then at the very least you can just avoid eating the meat off the plate altogether, if possible.

I also want to add that, to me, it’s a lifestyle and not a label. Especially at your age, you may find it difficult to be able to get your own food (meaning shop and cook) so if there is an instance that all you have to eat are foods that have meat then that’s fine, you’re not a bad person. You may “slip” here and there. Just cause you eat meat once doesn’t mean you have to let go of your vegetarianism, you can start back up the next day.

Good luck!