Allowing 16-year-olds to vote will make them more vulnerable to sexual abuse, an MP has said.
Labour's Barry Sheerman said the change "shrinks childhood" by making people adults at 16.
He spoke as MPs debated extending the franchise during the EU referendum, a move they then rejected in a vote.
Shadow Europe minister Pat McFadden said he respected Mr Sheerman but could see no link between extending voting rights and sexual abuse.
Huddersfield MP Mr Sheerman said: "Up and down this country we've had vulnerability to sexual predators and ghastly things happening right through to 18 and this move to have adults at 16 will make a lot of young men and women more vulnerable to sexual predation than that happens at the moment."
After Mr McFadden rejected this argument, Mr Sheerman added "what those of us - the small minority of us on these benches I have to say - worry about is" that if people are treated as an adult at 16 "that shrinks childhood".
Labour and the SNP support allowing 16 and 17-year-olds to vote in UK elections, but the government is against the policy.
Setting out his party's position, Mr McFadden said that aside from the wider debate about the voting age, there was a "very strong reason" to lower it for the EU referendum because young people's future was "directly at stake".
If the UK votes to leave the EU, their ability to live and study in Europe would be affected, he said.
But Conservative Cabinet Office Minister John Penrose said this was not the time to consider such a change, saying the issue should be "soberly and properly debated" on another occasion.
The change was rejected in a Commons vote by 310 to 265.
The bill, which will put into law the in/out referendum promised by 2017, is currently making its way through Parliament.
Also during the committee stage debate, an SNP motion to allow EU nationals resident in the UK to vote in the referendum was rejected by 514 votes to 71.