State laws dictate when employees get breaks and how long those breaks can be. Under these laws, employers need to provide a minimum amount of rest time, potentially including short paid breaks or paid lunch hours. In Missouri, however, that isn't necessarily the case for workers like you.
The Department of Labor shows the laws for lunches and breaks in the state of Missouri. In this state, there actually aren't any laws in place which protect a worker's rights to have a break. This goes for any kind of break, including lunches. Related to that, age doesn't impact whether or not you may get a working break. Even youth workers aren't guaranteed one.
Because of this, it's up to each individual company to decide what they will or won't offer when it comes to breaks for employees. They can choose to disallow paid breaks entirely, though most companies don't do this. Some may offer shortened lunches. Many companies comply with what is considered standard elsewhere, especially if it's a franchise with branches in other states with different break laws.
Most issues regarding violation of break policies in Missouri come from specific violations that only pertain to one company. For example, if you were promised a half-hour lunch break for every eight hour shift and you employer fails to follow through, then your terms of employment have been violated and you may be able to legally fight against this.
If you're facing a situation like the one mentioned above or anything similar, your next step may be to consider contacting an attorney experienced in wage and labor laws. They can help you fight for the breaks that you were promised.