I don't know if this has been addressed, but "Age of Marriage" and "Age of Consent" aren't mutually inclusive:
https://globaljusticeinitiative.files.wordpress.com/2011/12/united-states-age-of-consent-table11.pdf
This dichotomy isn't unique to the USA, either, apparently, so comparing the two isn't apples to apples; even if there are alarmingly anachronistic loopholes still on the books that technically allow for a very small number of Americans to potentially legally have sex with those below the age of consent, albeit still at least involving an 18+ adult involved in the process leading to that permission-- though I doubt any would consider this a sufficient legal protection of such minors today.
Mexico's federal minimum for Age of Consent isn't at all exonerated by the anachronism of a tangential American law, IMO.