When it comes to child pornography would a 20 year old get charged with child porngraphy if the girl was 17?

Yes, it is certainly a possibility, if the material falls within the definition of "pornography" either at the state level or federal and the person being depicted in the images is a minor under the age of 18.

Federal legal definition:

18 U.S.C. 2256 – “CHILD PORNOGRAPHY” DEFINED

Child pornography is defined as any visual depiction, including any photograph, film, video, or computer or computer-generated image
or picture, whether made or produced by electronic, mechanical, or other means, of sexually explicit conduct, where

• the production of such visual depiction involves the use of a minor engaging in sexually explicit conduct;

• such visual depiction is a digital image, computer image, or computer-generated image that is, or is indistinguishable from, that of a minor engaging in sexually explicit conduct; or

• such visual depiction has been created, adapted, or modified to appear that an identifiable minor is engaging in sexually explicit conduct.

In the state of Ohio there are several statutes regarding objectional or obscene materials and minors. These can be found in the http://codes.ohio.gov/orc/2907Ohio Revised statutes Chapter 2907 Sex Offenses (2907.31 through 2907.41). Child pornography cases can be charged at both the federal level and at the state level. Sometimes if the Feds decide not to pursue a case, the state will take jurisdiction.