QuestionI am a 14 year old boy. Should I cut my light-black colored mustache with scissors?
It depends on whether you want a mustache at this time or not. Most young men shave with a razor because the early facial hairs don't start all at once and the hairs tend to be lighter in color. Leaving them to grow just makes you look unkempt. Shaving keeps the hairs uniformly short. Generally by the time you are in your twenties, you will have enough dark hair on your face to grow a nice looking mustache or beard.
Scissors will take care of the few hairs that get way ahead of the rest of your hairs, but if you have the fine downy hair that first comes in (we call it "peach fuzz" in the United States), you won't be able to trim these with scissors close enough to make them unnoticeable. You'll have to use a razor and shaving cream.