Or just taxpayers and therefore those who contribute get the most say

It's a bit wrong that you can go out to work at 16 and drive at 17, but not get to vote for the MPs who make decisions on these matters until you're 18. However, the solution for me is to raise the mandatory education age and driving age to 18, rather than lower the voting age.

The age of majority does need to be reviewed I think.

At 16 you can join the armed forces and die for your country. At 16 you can have sex and raise a family. At 17 you can drive a car. You have to wait until you're 18 before you can vote.

If anything, I'd prefer to see all this reviewed and harmonised. My head tells me it really ought to move upwards, but I can see no real reason why it shouldn't go down.