Downing Street has distanced itself from comments made by Cabinet Office Minister David Lidington after he told a Labour frontbencher to "grow up".
Theresa May's effective deputy made the remark to Labour's shadow foreign secretary Emily Thornberry after she pressed him on the issue of lowering the voting age to 16.
The pair clashed as Mr Lidington stood in for Mrs May during Prime Minister's Questions in the Commons.
Ms Thornberry branded the Tories and the DUP a "coalition of cavemen" for their opposition to the change, telling them to learn the lessons from 100 years ago which ultimately secured women the vote.
Mr Lidington insisted Britain was in line with most countries on voting age.
He said: "The situation we have here with the national voting age at 18 is one that is followed by 26 of the 27 other members of the European Union, by the United States, Canada, New Zealand and Australia.
"Unless she's going to denounce all of those countries as somehow inadequate to her own particular standards, then quite honestly I wish she ought to grow up and try and treat this subject with a greater degree of seriousness."
Asked for Mrs May's take on Mr Lidington's "grow up" remarks, a Government spokesman said: "I think she wouldn't use that language.
"I think she would, however, agree with him that 18 is the right age at which people should be allowed to vote.
"I think the Prime Minister would agree with David Lidington that it is generally accepted in Britain that we reach adulthood at 18."