Lower it to 16, or 17 with parental consent, and at these ages they should only marry with someone no more than one year or two years older for safeguarding reasons.
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Many young people who are in comfortable relationships may want to get married. People who are of romany gypsy race or people who are religious or anyone else wanting to get married young have to wait a year or two. why not wait you ask? Well many people learn to drive and get jobs around 17, maybe they should also wait?