Question: Many countries have constitutional provisions which prohibit discrimination based on certain characteristics (i.e. age, nationality, etc) while also - within the same constitution - having restrictions on voting right based on the very same characteristics.

For example, in the Estonian constitution, [Section 12](https://constituteproject.org/constitution/Estonia_2015?lang=en#s40) states no one should be discriminated based on "nationality", "origin", or "other grounds". But later in [Section 57](https://constituteproject.org/constitution/Estonia_2015?lang=en#s201), it restricts voting right to citizens of age 18 or older - this seems to constitute discrimination based on "nationality" and age (covered by the catch-all "other grounds").

Does this mean these constitutions are contradicting themselves? How do legal scholars reconcile these seemingly paradoxical provisions within their respective constitutions?

Answer: 
"Nationality" is not the ethnic origin, it is largely the same as the citizenship (from the [dictionary](https://dictionary.cambridge.org/dictionary/english/national), *someone who officially belongs to a particular country, a citizen of a particular country*). Discrimination by ethnic origin is not allowed. Discrimination by citizenship is allowed and obvious: citizens can enter the home country without visa, vote, work with much less restrictions and the like. Discrimination of foreign citizens against each other, based on they citizenship, is also widespread starting from the queue in the airport upon arrival ("EU nationals go left, all other nationals go right").

Ethnic origin and citizenship is not the same, and the national is a citizen (the definition sometimes extends to people who live for many generations in the country without citizenship). A sentient green spider originating from Andromeda galaxy would be an Estonian national if given a citizenship for some reason. All ethnic Russians with Estonian passport are Estonian nationals. They are **not** Russian nationals (dual citizenship in Estonia is not allowed).

P.S. There is an English translation of the constitution [here](https://www.constituteproject.org/constitution/Estonia_2015.pdf?lang=en). Who does not know Estonian anyway, could probably rather read the translation.
There is usually an exemption to these constitutional bans on discrimination. Under the *lex specialis* rule, any form of discrimination that is specifically prescribed by law is not allowed, and often even mandatory. Voting booths **must** discriminate on age.

This is often implicit, both in the constitution and the law that establishes the exception. This unclear wording is often justified by legal precedent, a lot of this discrimination predates the various constitutions and many lawmakers did not feel obliged to point out the obvious limits. E.g. the Dutch constitution has an explicit exemption for the Freedom of Speech, but an implicit exemption for discrimination.