Begin by checking your state's child labor laws. Many states do not allow you to have a job until the age of 16, there are some, however that allows children to begin work at the age of 14.
Keep in mind that it is usually only fast food restaurants that hire this young, many retail stores will not hire under the age of 18.
Also, during the school year those ages 14-15 are allowed by the law to work only on the weekends.
If the idea is just to make a little pocket money babysitting, dog walking, pet sitting or offering to odd jobs is probably the best way to go.