Everyone is affected by government policy, but the disparity between representation and responsibility is greatest between those aged 16, who cannot vote, and those aged 18 who can.
Everything from education policy through to health and social policy can have an immediate effect on 16 year olds have no say in who represents them at a national and local level. At 16 a person can join the Army, but not vote. A 16 year old can work, but not vote. A 16 year old is old enough to be tried in a court and punished for breaking the law, but cannot vote.