During Prime Minister's Questions in the Commons, he made clear he thought 18 was the "right age" but stressed: "I'm very happy to listen to the debate, to listen to the arguments and to put them forward."
His comments came after Labour's John Robertson, who represents Glasgow North West, noted the involvement of young people in the referendum campaign and asked if it was "not time" for 16 and 17-year-olds to have the vote in the rest of the UK.
Mr Cameron replied: "The referendum campaign in Scotland did switch a whole lot of people on to politics and political issues because the question that was being asked was so important.
"Now, we've said that we should respect the views of the Scottish Parliament, the Welsh Parliament and we will devolve those powers over voting age.
"In this House, I'm very happy for us to have a vote. Personally, the right age is 18 but I'm very happy to listen to the debate, to listen to the arguments and to put them forward."
Following PMQs, when asked why the PM believed 16 and 17-year-olds should not get the vote at general elections, a No 10 aide said Mr Cameron did "not at this stage see a compelling argument to change existing legislation".
He said it was a matter of devolution that the Scottish Parliament got to decide on the franchise for the referendum and Holyrood elections.
Later, the PM's spokesman was asked if Mr Cameron would accept a Commons vote as binding but he appeared non-committal, saying there were different types of votes.
Meantime, Mr Robertson said he was very disappointed with the PM's response.
"During the referendum, we saw our young people play an incredibly important role not just voting but being active in the debate and in many cases working on the respective campaigns. If there was ever any doubt about the ability of our young people to rise to the challenge, then the referendum surely showed otherwise."
The backbencher said Mr Cameron's position led to the "ridiculous situation" in which 16-year-olds would be able vote for their MSPs but not their MPs.
"In the face of the evidence, why are the Conservatives still running from giving people who can already pay income tax and get married the chance to vote for their Member of Parliament? Are they scared they won't vote for them?" added Mr Robertson.