Age discrimination.

Whenever a government regulation or policy impacts a suspect class like race or a fundamental right, like marriage,  it is subjected to the strict scrutiny test in court which means that the government has the burden of proving that the regulation is necessary to achieve a compelling state policy objective. However whenever a government regulation impacts or discriminates based on the category of age, The burden of proof to uphold the Constitutionality of that law is the rational basis test, which only requires proof that the regulation is Rationally related to achieve any legitimate state purpose. Because children have a much lower incidence to contract Covid and if they contract Covid, they have a far higher recovery rate than an adult, the regulation would pass the rational basis test because the age discrimination is rationally relate to Protect both children and adults from the virus. But because children have more of a natural immunity from the virus than adults it isn't necessary for them to have a vaccine. Accordingly, The court would most likely uphold the law even though it discriminate based on age, because it is rationally related to the legitimate purpose as discussed above.