Good idea to document determination. - Particularly if you conclude you are not subject to the rule. - Not a rule requirement. See Section 2.4 of SPCC guidance document. http://www.epa.gov/emergencies/docs/oil/spcc/guidance/2_Applicability.pdf.
The age of consent is eighteen. With parental consent, parties can marry at age seventeen with the exception that if one party does not have a parent who resides in the state and one party has been a resident in Oregon for at least six months, then no permission is necessary.
The age-16 states tend to be smaller, so a little less than half the population lives in those 30 states. Over 60 percent of the population lives in the states that set the age of consent at 16 or 17, regardless of how one counts Texas. Nor is this some purely modern invention.