It's not about how much you know, 16 year olds don't care about voting because they are not directly affected by the decisions. It should be the age of majority.
The 16 year old lifestyle compared to the 24 year old lifestyle, is very different. It's a maturity, not to say there aren't mature 16 year old but it is definitely the minority who deem themselves mature enough to even consider voting.
The effort it would take the government to implement a new voting age isn't worth it.