There are two points.
One is that, really, there's a lot of evidence to the effect that 16-year-olds are still very vulnerable. I think 18-year-olds can still be very vulnerable. In the cognitive development of children and the social development of children, those are very critical years. I think that's a problem in itself.
The other problem you're going to face here, though, is that when you start putting in age units like that, you're going to be faced with more and more issues relating to the assessment of age in individuals. Sadly, Australia has really exhibited some of the world's worst practices in age determinations. But you're really creating enormous problems for your decision-makers in having to make a call.
People do not arrive with their birth certificates. Some countries, such as Afghanistan, don't even mark ages the same way we do, so age determination becomes a very imprecise science. You will end up with children aged 14 being assessed as being 16, 18, or 17. Once you put down age units at 16 like that, you're introducing all sorts of problems. Again, I think it's a very regressive measure.