From Miss Universe website:
ARE THERE AGE REQUIREMENTS?
Yes. Miss Universe and Miss USA contestants must be at least 18 and under 28 years of age before January 1st in the year they hope to compete in the Miss Universe or Miss USA pageant. Miss Teen USA candidates must be at least 14 and under 19 years of age before January 1st in the year they hope to compete in the Miss Teen USA pageant.
For the 2nd straight year another "underage" contestant will compete at Miss Universe pageant. This is Miss Belgium Zoé Brunet, she was 17 years old when she competed at Miss Belgium last January 2018.
Miss USA state pageants continued to use the strict age limit provided by MUO because there was Miss Teen USA pageant for those who fell short at the age limit for Miss USA. But it possibly seemed that MUO had adjusted the minimum age limit from at least 18 to at least 17.5 (17 years and 6 months) of age before January 1 just to give favor to some underage contestants at the pageant like Monalysa in 2017 and Zoe this year? If this is true more "underage" girls outside USA will compete at the national pageants for Miss Universe aside from allowing transgenders with legally female to compete?