While I don’t fundamentally disagree with the points made (some are very valid), this argument misses a key point.
At 16, often for the first time, young people are making big decisions that will have a profound effect on their long term future. As with any decision making of importance external factors will need to be considered and a big one is the current political landscape.
The missing point is the future. In order to make decisions about their future, young people need to have awareness of the political landscape affecting them. They will begin to form opinions based on the political decisions that they can see and feel affecting them and their choices.
It is at sixteen that young people will often begin to engage in politics because they see it’s direct impact on their futures. It is at this point, when politics begins to affect them individually that they should have their say on what the effect is.