lower the voting age to 13.

Let's face it: as time moves on, the age of education and maturity lowers. I've met children under the age of 10 that swore and/or understood sex somewhat.
Apart from that, children have become smarter and more politically aware. My friends and I have strong political beliefs, and even define ourselves under parties, economic beliefs, etc., and we are in middle school.
The entrance to adulthood is generally considered when a child becomes 13. In some cultures, that's when a child becomes an adult. And at that time, a child may start to develop politically beliefs and have a desire to be an influence in the people's voice.
Many votes do not exist simply because the voter isn't old enough to vote, and this could be solved. I highly recommend lowering the voting age from 18 to 13.