Children who have responsibility in their communities will be responsible.
Right now, I am writing an article about emotional immaturity, and it almost every time starts in the childhood. What you say about letting kids assume responsibility is extremely important, it will help them later on in life.
Honestly, I would be quite content to end legal age limits for driving, drinking, and voting
Voting is very delicate, there are a lot of problems all over the world because people vote for things they don't understand, and young people tend to be really misinformed about political mistakes from the past especially if they happened in other countries, and they tend to adopt certain tendencies that were already prove as something that always fails.
Starting early to be responsible for themselves and for their community may well be the most important thing.
I think the problems we see with voting is at least partly because children have no practice at it. Of course it's also because people are often so weirdly secretive, so no one is really teaching anyone about how to understand the issues and look beyond lip service, etc. For that matter I see an awful lot of politicians also remaking old mistakes and trying to continue on with clearly failed policies. Of course that is probably intentional.
What I always saw at any Sudbury school I went to was that children took their responsibilities very seriously. They wouldn't vote if they didn't understand, and they always listened through the meeting to different sides before voting if they were going to vote. With staff elections, they were always quite aware of what was at stake there - from the proper running of the school to someone having a job to provide for their family. I found them to often be more thoughtful than adults, especially the younger ones.