Two years ago when our daughter was one month into her 16th year she was in a relationship with a male whom we thought at the time was 18. A year later we found out it was sexual and that he was actually 21. She ended up pregnant and had a baby at the age of 17. A few months ago we really found out his age is 23 at this moment. My question is this, can we bring criminal charges against him for having sex with a minor?

Yes, you have the right to file a complaint against him with the authorities and/or the District Attorney's office directly (depending on local procedure). The District Attorney would examine the evidence and determine what violations occured and what charges (if any) should be filed against him. It appears that you are within the statute of limitations for certain offenses against a minor. These are listed below. Ultimately, the DA makes this determination when charges are filed.
Sources and links to Oregon Criminal Code are located at the bottom of this page.

Oregon Criminal Prosecutions: Statute of Limitations
Citation: Rev. Stat. § 131.125

The statute of limitations for certain offenses is a period within 6 years after commission of the crime.

If the victim was under 18 years of age at the time of the crime, the statute of limitations is anytime before the victim attains 24 years of age, or within 6 years after the offense is reported to a law enforcement agency or other governmental agency, whichever occurs first. The offenses included are:

• Criminal mistreatment in the 1st degree
• Rape in the 1st to 3rd degree
• Sodomy in the 1st to 3rd degree
• Unlawful sexual penetration in the 1st or 2nd degree
• Sexual abuse in the 1st or 2nd degree
• Encouraging child abuse in the 1st degree
• Incest

The statute of limitations for certain offenses may extend for a period within 12 years after commission of the offense if the defendant is identified after the statute of limitations period originally prescribed for the offense on the basis of DNA sample comparisons. The offenses included are:

• Rape in the 1st or 2nd degree
• Sodomy in the 1st or 2nd degree

The statute of limitations for certain offenses extends for 4 years after the commission of the crime or, if the victim at the time of the crime was under 18 years of age, the statute of limitations is anytime before the victim
attains 22 years of age, or within 4 years after the offense is reported to a law enforcement agency or other governmental agency, whichever occurs first. The offenses included are:

• Sexual abuse in the 3rd degree
• Furnishing obscene materials to minors
• Sending obscene materials to minors
• Exhibiting an obscene performance to a minor
• Displaying obscene materials to minors

Generally, the following statutes of limitations apply:

• For a felony, it is a period within 3 years after commission of the crime.
• For a misdemeanor, it is a period within 2 years after commission of the crime.

Civil Actions
Citation: Rev. Stat. § 12.117

• The statute of limitations for filing a claim based on conduct that constitutes child abuse or conduct knowingly allowing, permitting, or encouraging child abuse will not begin for a minor entitled to file a claim until he or she reaches 18 years of age, and it will not run for longer than 6 years after he or she reaches 18 years of age.
• If the minor has not discovered the injury, and in the exercise of reasonable care should not have discovered the injury or the causal connection between the injury and the child abuse, the statute of limitations will not run for longer than 3 years from the date the minor discovered or should have discovered the injury or the causal connection between the child abuse and the injury, whichever period is longer.

Sources
Oregon Criminal Code Chapter 163.305 Sexual Offenses [1]
Oregon Criminal Code Chapter 131.125 Time Limitations [2]
Childwelfare.gov [3]


Other possible related recources
Oregon Division of Child Support [4]
Oregon.gov Children & Teens [5]