Boosting the youth vote would have only a marginal impact on the result of a General Election, a new report has found.
But in a tight contest like 2015, getting 18-to-34-year-olds out to the polling stations in similar proportions to the over-65s would have been enough to deny David Cameron his overall majority - while costing Nick Clegg his seat and saving Ed Balls.
The research was released on the final day to register to vote for the June 8 General Election.
Its findings suggest Labour is right to encourage young people to register, as Jeremy Corbyn's party is the most likely to benefit from a strong youth turnout.
But it poured cold water on expectations of a transformative impact, finding that just 11 of the 573 constituencies in England and Wales would have had different results in 2015 if the 18-34 turnout had matched the 78% of over-65s who cast their ballot.
In fact, just 43% of 18-to-24-year-olds and 54% aged between 25 and 34 voted.
Voters over 55 outnumber younger voters in 445 English and Welsh constituencies, found researchers from the International Longevity Centre UK. And in 118 seats, there are more than twice as many over-55s as younger voters.
And the political power of older voters is likely to be consolidated further due to a forecast decline in the number of younger people in the UK by 2050, in a period when the number of over-65s is expected to rise by almost 70%.
ILC-UK assistant economist Dean Hochlaf said: "While attempts to get young people to vote are encouraging, we need to do more to stimulate active engagement in politics.
"An ageing society is going to put more pressure on government resources and voters will be taking this into consideration when they cast their ballots.
"The challenge for young people is: how do they take their case to the rest of the electorate for policies that are going to benefit their generation and build a more inclusive society? This might not be the easiest task, but it will be impossible if young people continue to be left out of the political debate."
Using data from pollsters Ipsos MORI and the Office for National Statistics, the ILC-UK researchers found that nine Conservative and two Liberal Democrat constituencies would have swung to Labour if younger and older voters had turned out in similar proportions in 2015.
Among them are Morley and Outwood - which Mr Balls lost by a margin of just 422 - and Mr Clegg's Sheffield Hallam.
Other seats which would have gone to Labour were Plymouth Sutton & Devonport, Derby North, Croydon Central, Gower, Brighton Kemptown, Thurrock, Vale of Clwyd, Bury North and Leeds North West.
Rather than having a clear majority with 330 of the House of Commons' 650 seats, Mr Cameron would have been left with just 321 MPs and been forced to seek some sort of deal - possibly with Northern Irish unionists - in order to hold onto power.