My personal view on the world is that it's always better with a bad but democratically elected government then a good one that isn't.
So from my point of view anyone with a genuine opinion and that is affected by a governments decisions directly that live in the country and have lived there a while should have voting rights.
Off course I do see the point that it might not always be possible.
For instance I can easily picture kindergarden kids being bribed to vote for a party with sweets (not that the political parties don't try to do the exact same thing with grownups, but still)
At any rate maturity comes with experiences (don't need to have anything to do with age)
And why should a government try to pick out who is mature enough to vote or not?
If they do it by age it will be unreliable because age don't actually equal maturity and if you do it by experience you're discriminating against people with a different set of experiences then you and the lack of diversity will apart from making your society less stable also no longer be a true democracy and therefore not have legitimacy.
Meaning that anyone who's views are not represented in a government have the right not to acknowledge the government.
Well, that's my two cent.