If a boy 17 yrs of age, had sex with his girlfried who was 3 days away from her 15th birthday are there possible charges. This was a "consentual" yet stupid act. And what evidence would be neccessary to file charges.

There could be action taken through the juvenile justice system based on current state laws. Any action or penalty would be determined by a juvenile court judge. In the case of a pregnancy, a judge could rule that it be moved to adult court. aside from pregnancy, other evidence a judge might consider would be if they were "caught in the act" or someone witnessed the two of you together.

Article 7A Rape and other Sexual offenses including Statutory Rape
Note: Consent is no defense, although marriage is generally a defense.

First Degree Rape [GS 14-27.2(1), Class B1 felony]
Vaginal intercourse with victim under age 13 by defendant at least age 12 and 4 years older.

First Degree Sexual Offense [GS 14-27.4(a)(1), Class B1 felony]
Sexual acts (not vaginal intercourse) with victim under age 13 by defendant at least age 12 and 4 years older.

Statutory Rape by 13, 14 or 15 year old [GS 14-27.7A, Class B1 or C felony]
Vaginal intercourse or sexual act with 13, 14 or 15 year old by defendant 5 years older (Class C felony) or by defendant at least 6 years older (Class B1 felony).

Indecent Liberties with a Child (adult perpetrator) [GS 14-202.1, Class F felony]
Indecent and lewd acts with a child under age 16 by a defendant at least 5 years older.

Intercourse and Sexual Offense with Certain Victims [GS14-27.7(a), Class E felony]
Vaginal intercourse or sexual act by caretaker with a minor residing in the home, or by an agent of an institution or person having custody of a victim of any age.

Indecent Liberties with a Child (juvenile perpetrator) [GS 14-202.2, Class 1 misdem.]
Indecent and lewd acts by a defendant under age 16 with a victim at least 3 years younger than the defendant.

Indecent Liberties with a Student [GS 14-202.4, Class I felony or A1 misdemeanor]
Indecent and lewd acts by a teacher, administrator, or coach with a student at the same school, when the perpetrator is 4 or more years older than the victim (Class I felony) or less than 4 years older (Class A1 misdemeanor).

Intercourse and Sexual Offense with Certain Victims (schools) [GS14-27.7(b)]
Vaginal intercourse or sexual act by a teacher, administrator, or coach with a student at the same school, when the perpetrator is 4 or more years older than the victim (Class G felony) or less than 4 years older (Class A1 misdemeanor).

Computer Solicitation of a Child [GS 14-202.3, Class I felony]
Computer solicitation of a child for sexual purposes by a perpetrator at least 16 with a victim under age 16 and at least 3 years younger than the perpetrator.

Other laws:
Article 26 Offenses Against Public Morality and Decency
Note: Consent is no defense.

Crime Against Nature [GS 14-177, Class I felony]
Oral sex, anal sex, sex with objects by unmarried persons, and bestiality. 5

Fornication and Adultery [GS 14-184, Class 2 misdemeanor]
Unmarried persons who have engaged in “lewd and lascivious” association or cohabitation together, or by a married person with another not that person’s spouse. 6

Incest Between Near Relatives [GS 14-178, Class F felony]
“Carnal” intercourse with grandparent, parent or sibling.

Incest Between Uncle and Niece or Nephew and Aunt [GS 14-179, Class 1 misdem.]
“Carnal” intercourse between uncle and niece or nephew and aunt.

Opposite Sexes in Same Hotel Room [GS 14-186, Class 2 misdemeanor]
Opposite sexes occupying the same bedroom at a hotel for immoral purposes; or falsely registering as husband and wife at a hotel.