I went vegan hen I was 15 and didn’t bother asking. Veganism is a moral imperative and as such the need for people to stop exploiting/ raping/ murdering etc others trumps whatever your parents say. I just did it, my mom hated it (still does for the most part) but I just stuck it out and did whatever I needed. If you run into resistance at first just do whatever you have to do because whatever happens as a result probably wouldn’t be that bad in all honesty and would be nothing compared to what happens to the nonhuman victims if you go back.
when i asked my parents if i could go veggie my step mom was already veggie so she said i could try it at first i didn’t know what to try because i wasn’t sure if i would like it. I tryed it and i did like it people at school would say tofu was gross and teachers would ask how i got my protein it made me so much but i soon got over it and ignored those people. Today i’m proud to be veggie and i’m never going back!
Ignore the troll who has nothing valuable to do with their time. As for asking your mom just tell her you want to do more for helping the animals. If she is worried about you getting enough nutrition tell her you can get calcium from nondairy milks and iron from lots of greens. Show her forks over knives and show her there are lots of benefits to a vegan diet. The best approach is to be knowledgable and reasonable. If she says no at first try to find out why instead of turning it into a fiery argument. Hope this helps.