There are administrators who are over 18 years of age and are worse than a baby
also it is not difficult to lie about age.
i have seen this on some servers: place a hidden word in the rules, and in the admin request force the player to write the hidden word. If they cannot answer or write a wrong word they will be rejected
This works for most kids
remember to change the hidden word every few days
the only problem: if a person does not have a basic knowledge of english they will not understand or will not be able to answer (but any "mature person" would answer without any problem)
that is just my opinion