You've grown, and during that time, you have learned to crawl, walk, run, ride a bike/skateboard/etc. all while doing so with sidewalks and roadways as part of the regular run of the day. The next logical progression is to start driving a vehicle on those roadways.
In truth, the ability to drive has become more restricted, with limits that were not in place in years past being placed on new drivers, to further acclimate them to the responsibility of driving.
The responsibility to vote is much greater than being able to properly make a left turn. You should be looking at more than what you want right now, which is what most teenagers (granted that not all are like this) are thinking about, especially in this day and age of instant self gratification. Most teenagers, hell, most adults, do not put in the work required to make an actual, educated, vote.
In truth, the voting age should probably be raised.
I would be interested in some type of evidence from you showing that someone age 17 was able to join the military and die for their country without somehow lying about their age. Maybe in the case of an emancipated youth? But the general rule is you can sign up for delayed enlistment at 17 with a parent consenting, you will then ship out to basic once done with high school (which most children are usually 18 by then, my son was an exception), and by the time you are done with basic training and tech school, you will be 18. Before you go off and die for your country. Your point about 17 year olds voting because they can join the military is not strong.