You are comparing apples and coconuts here.
Voting is a civic act, criminal acts are, well, criminal and it’s not (yet) a crime to vote.
While young people are still developing and maturing, we generally allow them some leeway and understanding in the choices they make. When those choices result in a crime being committed, they still face the judicial process but with due consideration being given to their age before passing sentence. They will indeed be held ‘responsible for their criminal actions’ and the judge’s sentence may take their level of maturity into consideration or not, since this is only a guideline and the full range of sentencing always remains available.
So, people under 25 who are convicted of a crime are still held responsible, as evidenced by their conviction, it’s only the sentence that might be varied depending on their assessed maturity.
Are you in favour of aligning the ages for criminal and civic responsibility?