One thought to support your argument might be precedents set in other legal matters: Citizens are allowed to drive at age 16 (in most states), because they are considered responsible enough to handle the obligations that come with vehicle operation. If a person is thought to be credible enough to operate a piece of machinery that could potentially be responsible for multiple deaths, surely then they can be considered mature enough to make a decision regarding national, state, or local leadership. In many states, pilot's licenses are also granted as early as age 16. The same logic applies.
I have 4 arguments for you. Perhaps some of these will help.
1) Studies have long suggested that it is important to begin the voting habit early, or voters are likely to be lost to the electorate. If young people feel disenfranchised at a time when they are interested, they are more likely to avoid voting later.
2) Young people have recently been more involved than ever in electoral politics, and have earned the right to vote.
CIRCLE estimates that youth voter turnout rose to between 52 percent and 53 percent, an increase of 4 to 5 percentage points over CIRCLE’s estimate based on the 2004 exit polls. The 2004 election was a strong one for youth turnout, reversing a long history of decline. If we compare 2008 with 2000, the increase in youth turnout is at least 11 percentage points. This year’s youth turnout rivals or exceeds the youth turnout rate of 52% in 1992, which is the highest turnout rate since 1972 (55.4%).
3) Young people have a big stake in electoral politics. The actions of those elected when you are 16 or 17 will determine the political and economic climate when you start your adult life.
4) At age 16, you can work, pay taxes, and drive. You can even be charged as an adult for a crime – and get the death penalty! How can we say someone 16 should be vulnerable to the death penalty as a ‘mature, responsible adult’ and then say people the same age are not mature enough to vote?
The world we live in is becoming 'smaller' everyday, and regardless of whether it's good or bad, right or wrong, young people today are bombarded with external experiences so different from prior generations the reality of their life experiences (the events of 9-11,terrorism,enviornmental destruction, the deficit... could perhaps dictate a dawning of a new political perspective. If one sided with this reality it could support an argument to lower the voting age to 16.
You could use that people mature faster. The ability to comprehend driving materials and being able to react instinctively should allow people the capacity to discern political issues. Young adults can also work, entailing them to understand complicated processes and procedures at work, and being exposed to different occupations for a job would hopefully prepare them for understanding political issues.
The justification of a minimum age for voting is that younger people are not mature enough to decide on who should be put in charge of governing the country. So if you you want to support the proposition that the voting age should be lowered to 16 years, you can make your arguments more effective by providing examples of achievements and activities of children of 16 or less that prove that they possess acceptable levels of maturity for voting.
At the age of 16, young adults can drive a car, get a job, and make their own decisions about their schooling. Getting the right to vote at 16 would also make teenagers feel more responsible in desicion making.
Teenagers who could vote at 16 would possibly cause a higher voter turnout during elections.
Most importantly, teenagers would be more interested in the government since they would have a say in it as well.