Under plans to be put before ministers next year, a Representation of Young People Bill would allow the UK's 1.5 million 16 and 17-year-olds to vote in general and local elections.
Advocates of the change said yesterday it was simply "absurd" that the law allowed youngsters to pay tax, have sex, get married and fight for their country but denied them the franchise.
The cross-party move follows a new study that shows teenagers are much more interested in politics than commonly assumed, even though many are disillusioned with the main parties.
Labour backers of the idea believe it could restore much-needed idealism to the Government's battered image and confirm Tony Blair's reputation as a ground-breaking premier.
The last lowering of the voting age, from 21 to 18, was enacted by Harold Wilson's Labour government in 1969.
A Home Office working party on electoral law will be presented with the proposals next summer once it has concluded its current consultation on electronic voting and polling stations in supermarkets.
Labour won the last general election with the help of a large lead among young voters and party officials believe the age change could help it to hold on to scores of key marginal seats.
Pressure to extend the franchise age follows research by Loughborough and Nottingham Trent Universities into the attitudes of under-19s.
The study, backed by the Labour-supporting Fabian Society, found that more than 81 per cent discussed politics with family or friends and three-quarters thought it was important to vote in national elections.
The survey, which polled 5,000 teenagers to make it the biggest of its kind conducted, found that just 5 per cent thought voting was a "waste of time". Tackling poverty was their top political priority, followed by help for the Third World and care for the environment.
Dominic Wring, one of the study's authors, said the research had uncovered evidence that teenagers exhibited an "engaged cynicism" about politics. They were disillusioned, but wanted a greater say.
"Tony Blair, like no prime minister since Harold Wilson, has talked of a `young country' whilst cultivating and listening to celebrities popular with youth," he said.
"Fundamentally something more imaginative and concrete is required to sustain and nurture democratic participation among the young. A progressive administration would adopt this."
Although Labour stands most to gain from an expanded youth vote, the Tories and the Liberal Democrats believe under-18s could reap them electoral dividends.
Policies such as the lower minimum wage rate and benefit restrictions for the under 18s, as well as rising unemployment, could lead to a backlash against Labour, they say.
Lembit Opik, MP for Montgomeryshire and the Liberal Democrats' Youth Affairs spokesman, said his party was the only one formally committed to lowering the voting age.
"The simple fact is that people under 18 feel that they are prejudiced against in grounds of age. They pay tax, can have sex and die for their country, but they can't vote. It's a classic case of taxation without representation.
"The onus is on those who want to keep the voting age at 18 to prove why they are right, not on those who want change."
Legal Rites of Passage
At age 13:
Allowed to get a part-time job.
Allowed to go into a pub;
own an air rifle and its ammunition; be employed on a weekday as a street trader by your parents (subject to local authority by-laws).
Allowed to leave school;
Get married with parental consent (without consent in Scotland); buy tobacco;
Consent to heterosexual intercourse (girls); join the armed forces with parental consent (boys); drive an invalid carriage or moped;
Drink beer or cider with a meal in a restaurant; buy lottery tickets and scratchcards; buy liqueur chocolates; enter or live in a brothel; become a street trader.
Can be interviewed by the police without "an appropriate adult" being present;
Join the armed forces with parental consent (girls);
Hold a licence to drive most vehicles.
Allowed to vote; serve on a jury; buy and drink alcohol in a bar; consent to a "homosexual act" with another man in private; get married without parental consent; own land and apply for a mortgage; enter a betting shop and place a bet; get a tattoo; give your body to science; buy fireworks.
Become an MP; hold a licence to drive a large passenger vehicle or heavy goods vehicle; apply for a licence to sell alcohol; adopt a child.