Sure!
One reason may be that persons younger than 18 will not always make responsible decisions, so entrusting them with electing officials might not be prudent.
A person younger than 18 might not vote for themselves, to reflect their own beliefs, but they might be influenced or even pushed to vote for a representative or measure of their parents' choosing.
People younger than 18 generally are not educated enough about politics and policies to make smart choices when it comes to voting.
Hope this helps!