A private pilot license or certificate is one of the requirements to obtain your commercial pilot license. The FAA in the US, JAA/EASA in Europe, CASA in Australia, or Transport Canada in Canadia Canada, issues PPLs but each organization has different requirements. Here in the US, FAA requires you to be at least 17 years old and must have at least passed the knowledge and practical tests they administer. Find out the requirements on the organization webpage of your country.

To attain a CPL, you need to meet on the course entry requirements. The requirements include minimum age of 18, first class medical certificate, and a private pilot license (PPL) all which can be found here. With a CPL, you can act as a co-pilot in commercial air transportation and act as pilot in command of any single pilot airplane or helicopter. More information can be found here. Google is a good search engine to find more information as well, since some sites don't have specifics about CPL and general information about commercial pilots.

Generally, a college degree is recommended if you want to go further in aviation. If it is a requirement where you are applying to, make sure to meet the requirements. For example, Northwest will not consider applicants without a four-year college degree, while some other airlines may not require a college degree. It does not necessarily matter what college degree you get or the major you get a degree in. Some pilots have business majors, while others have degrees in Aeronautical Science. It all depends on what interests you and what you want out of it. Take a look here to get a better perspective on college education.