If Line is allowing 14 year-olds to earn money, it has either put in a lot of legwork to ensure that they meet the requirements for employing someone of that age (a quick Google search suggests that Korean labour laws permit 12-14 year-olds to engage in very light work, as long as their studies are not disrupted), or they are flat-out breaking the law.
Honestly, regardless of how mature a minor might seem or how immature an adult might seem, there's no realistic way to judge maturity on a case-by-case basis, so the laws provide a hard limit that apply to most of the population. If anything, a minor who is more mature than their peers due to hardships is more vulnerable to exploitation.
The problem here isn't the law, or the companies that have to follow it, the problem is your parents. A computer is an important and useful thing for you to have, even if you weren't making comics. They should either buy you one, or provide you with the opportunity to earn one, either by permitting part time work or by paying you for chores. Have you spoken to them and explained what you want to do? Most reasonable people would support a teenager saving up for something expensive but practical, because it's good practice for managing your money, and you're only a couple of years off potentially going to college or getting a job, where you'll have to manage it yourself anyway.
If they won't agree to that, well, they can't stop you from drawing altogether. You can always keep practicing using traditional media until you're in a position to get your own computer. You can even offer commissions to friends and family.
