OK, I'd take a compromise. If they're in the army they can vote. If they're not, they have to wait until they're 18. (also important to note, they can't be on armed operations when under 18)
Most 16 year olds are not productive members of society (the whole point of the tax comment) and yes, even tourists pay taxes, but not in an important way. 16 year olds are (mostly) dependent upon their parents still and they have zero experience or knowledge to base voting upon. I have a 15(about to turn 16) year old and a 17 year old and I know all their friends. They're not at an age where they could/or should be expected to vote responsibly.
There is no benefit to the country or to 16 year olds to give them the vote. It's not like there is no-one looking out for their interests, they're still dependent on their parents (most of them) and their parents will still be voting on their families' interests. They're not an overlooked minority denied a vote- they're just kids. (and that's not me being dismissive, that's the UK legal definition of a child, anyone under 18)