"We surely should not be preventing a section of the population from voting because we don’t like the way we think they might vote?"
No - we should not be preventing a section of the population from voting because of the way they vote, they should not be allowed to vote because they are children.
People are considered as adults in the UK when they are 18, and that is the age they become eligible to vote - I see no meaningful reason to change this.
Society deems that a 16 year old is not mature enough to buy fags, buy a pint of beer in the pub, leave education (in most circumstances - before somebody points out the few situations in which they can), get married without their parents permission, other than for necessities cannot enter into commercial contracts, so I fail to see why they can be considered mature enough to vote.
And if 16 year olds are allowed to vote, should 14 year olds be allowed? Or 12 years olds? If not, why not?
This is simply a cynical move, as a rule usually trotted out by Labour, because they know 16 year olds tend to be more left-leaning - I certainly was when I was in the 6th Form.