I don't know about the UAE, but in the US, most states have some lower age of consent to sex for married people, and I assume that normally marriages from abroad would recognized. So I'd guess that as long as you were having sex with someone you were married to and it met that lower bar for age, you could still have sex with them.

https://en.wikipedia.org/wiki/Marriage_age_in_the_United_States

https://en.wikipedia.org/wiki/Age_of_consent_in_the_United_States

So, for example, for Illinois's age of consent, the age is lower if the people involved are married:

The law allows the actor a defense to prosecution if the victim is currently or was previously married (the absolute minimum marriageable age in Indiana is 16[170]), although this defense does not apply in the case of violence, threats or drugs.

Whereas normally, the age doesn't go below 18.

I'd expect that Illinois would still potentially charge people who were legally married abroad to, say, a 14-year-old and then have sex with them in Illinois.

Specifically for immigration -- not just visiting the US --it looks like US immigration considers whether marriage would be legal at the age in question in the intended state of residence.

https://www.uscis.gov/archive/uscis-strengthens-guidance-for-spousal-petitions-involving-minors

Interviewing earlier at the I-130 petition stage provides USCIS with an additional opportunity to verify information contained in the petition and assess the bona fides of the claimed spousal relationship. USCIS officers will now conduct interviews for the following I-130 spousal petitions as part of the adjudication of any I-130 spousal petition where:

• The petitioner or the beneficiary is less than 16 years old; or
• The petitioner or the beneficiary is 16 or 17 years old and there are 10 years or more difference between the ages of the spouses.

While there are no statutory age requirements to petition for a spouse or be sponsored as a spousal beneficiary, USCIS published guidance earlier this year detailing factors that officers should consider when evaluating I-130 spousal petitions involving a minor. USCIS considers whether the age of the beneficiary or petitioner at the time the marriage was celebrated violates the law of the place of celebration. Officers also consider whether the marriage is recognized as valid in the U.S. state where the couple currently resides or will presumably reside and does not violate the state’s public policy. In some U.S. states and in some foreign countries, marriage involving a minor might be permitted under certain circumstances, including where there is parental consent, a judicial order, emancipation of the minor, or pregnancy of the minor.

A related topic where legalities differ between countries: polygamy. I'm pretty sure that I recall reading that if you immigrate -- not just the same thing as traveling to -- the US, and are in a polygamous relationship, you are required to only choose one spouse to be your wife under US law.

kagis

Yeah:

https://www.quora.com/Does-the-US-recognize-polygamous-marriages-from-other-countries

For example, a refugee who was practicing polygamy before he immigrated will be required by U.S. immigration law to designate one wife as his legal wife to accompany him to the United States. Years later, after becoming a U.S. citizen, he might divorce that wife, and marry the woman who was formerly his second wife, in order to petition for her (on Form I-130) to immigrate to the United States.

If the petition is approved, the new/formerly second wife immigrates, and then USCIS learns that the husband is still continuing to live with the first wife (even if only some of the time), all three could be accused of practicing polygamy. This is the case because all three come from a country where polygamy is practiced. Therefore, if the man lives with both women at the same time, whether the women live separately or apart, their joint behavior meets the USCIS definition of polygamy.

Similarly, if an immigrant from a country where polygamy is practiced culturally but not legally goes through a ceremony of customary ‘marriage' with someone in her country of origin who has other customary wives, USCIS will see her as a practicing polygamist. This will be the case even though there is no legal marriage between the couple, and even though she is living in the U.S. and he and his wives are living outside the United States.

Islam is the most common religious tradition recognizing the custom of polygamy today. Nevertheless, as a result of the biblical practice of polygamy, there exist practicing polygamists in both the Hebrew and Christian traditions. In addition, many African and some South-East Asian nations have sociocultural traditions of polygamy.

If you belong to any of these traditions (or certain sects within them), therefore, USCIS will pay close attention to indications that your household situation fits the definition of polygamy.

Because many immigrants and U.S. citizens come from religious traditions that have practiced polygamy, it is not against U.S. law to believe in polygamy, so long as you are not actually practicing it.

If you practiced polygamy before immigrating to the United States, but neither you nor your spouse(s) have practiced it since becoming a legal permanent resident, your prior history of polygamy should not cause your naturalization application to be denied.

If you have personally practiced polygamy since immigrating to the United States, (even if it was many years ago) you should not apply to naturalize without first consulting with an immigration attorney. Practicing polygamy as a legal resident of the United States will not only likely result in denial of your naturalization application, but grounds for deportation.

If you have not personally had multiple spousal relationships at the same time, but you have had a relationship with someone you considered a spouse (whether that relationship was legally recognized or not) and that person had other spousal type relationships at the same time, USCIS may determine that you are a polygamist. This is true regardless of whether your partner was living in the U.S. or abroad. It is especially true if you or your partner come from a country where polygamy is practiced, whether legally or culturally. You should definitely not apply for naturalization without first terminating that relationship (or making certain that your partner has terminated all other relationships). You should also wait to apply for naturalization until five years (or other applicable good moral character period) after the end of the relationship, unless you have a good explanation for why you got involved in the relationship; an explanation that makes it clear you did not intend to practice polygamy.

If you knew your partner was a practicing polygamist, or if you want to apply without waiting, you should definitely consult with an immigration attorney first.

Remember, USCIS examining officers are trained to spot polygamous behavior in applicants for naturalization who come from countries where polygamy is part of the culture. If you were knowingly involved with polygamy or polygamists, your application for naturalization is at risk of denial no matter who you were in the web of relationships.

EDIT: Under certain specific situations, some states have no minimum age for marriage in the US -- one could, hypothetically, become legally married to a four-year-old in California. Under the Full Faith and Credit Clause, all states are required to honor marriages performed in other US states, so someone can become married in State A and then move residence to State B. Thus, I'm pretty sure that it's possible to be legally married to someone in a state where one could not actually become married to that person, and still be legally prohibited from having sex with them while in the territory of that state.