Sixteen-year-olds could be given the vote in a referendum on whether to give Welsh ministers tax-varying powers.
The Welsh government will be given the right to decide the age at which people can vote in such a poll, Wales Office Minister Baroness Randerson said.
In the Scottish independence referendum in September, 16-year-olds were able to vote for the first time.
However, the voting age for assembly and general elections will remain unchanged at 18.
The change was announced in the House of Lords on Tuesday as an amendment to the Wales Bill, which will grant limited tax-raising powers to the Welsh government, including the power to amend income tax rates subject to a referendum.
Welsh Secretary Stephen Crabb said: "I know that there are strongly held views on allowing 16 and 17-year-olds to vote in a referendum but I have listened to the views in the House of Lords and decided that this is a matter on which the assembly should decide.
"The assembly has the power to call an income tax referendum - and it is right that they decide the age of those who can vote on this issue."
Steve Brooks, director of the Electoral Reform Society Cymru, said he "warmly welcomed" the decision.
"The inclusion of 16 and 17-year-olds made a huge difference to democratic engagement in Scotland, and is likely to have a lasting impact. This could make for a similar transformation in Wales.
"It is vital that steps are taken to ensure that young people are registered in schools and that civic studies are made a core part of young people's education to make the best use of this historic opportunity."