This year marks the 65th anniversary of the end of the Second World War. As the baby boomer generation, born between 1946 and 1964, moves towards retirement, it's worth reflecting on what that means for British culture and politics.

The baby boomers have always had a clear enough identity. Politically, they fought great ideological battles. Culturally, they stood for rights and freedoms. The big question now concerns the generation that follows: how will we choose to define ourselves?

For my grandmother's generation, to reach the age of 65 was some distinction. Today, it may mark the beginning of decades of comfortable and active retirement. Baby boomers still dominate British society: pop svengalis, journalists and CEOs continue to do their thing, seeing the 65th birthday as an increasingly artificial rite of passage.

Yet gradually we are seeing a new generation beginning to make its mark as it takes up prominent positions in British society. The editors of both this magazine and its biggest rival are now Generation Xers. Jack Dorsey, the founder of Twitter, is 34, Mark Zuckerberg, his counterpart at Facebook, is even younger, and Gary Lineker has long since replaced Des Lynam on the Match of the Day couch.

Westminster faces its own version of this momentous shift as a generation of politicians is set to exit the stage. Of the 121 MPs standing down at the next election, nearly three-quarters belong to the baby boomer generation, born in the aftermath of the Second World War. Their likely successors are younger candidates, those who belong to Generation X, born in the late 1960s and 1970s.

The template. And the challenge

This has profound implications for Labour. For two decades, our party's leading lights have been drawn from the baby boomers: Tony Blair, Gordon Brown, Robin Cook, Jack Straw and Harriet Harman, among others. Today it leans heavily on that generation.

Peter Mandelson remains one of the party's finest political minds and its key strategist. Ken Livingstone has dominated city government for the past 30 years. Jon Cruddas continues to mine Labour traditions for intellectual renewal.

But Labour's baby boomers cannot be expected to win the next election single-handed. Nor should they be expected to shoulder the burden of shaping an agenda for a fourth term alone.

For Labour's next generation, it is a moment of reckoning. Having spent our early adult lives under Tory rule, we have been fortunate to reach political maturity in government. Now if we want a fourth term that makes a real difference to the country, it is time for my generation to step up.

In the short term, that means everything to win the most important election since 1997. Beyond that, it means having the courage to move beyond the assumptions of the past 16 years, and to consider what an energised and intellectually confident centre-left party looks like in modern Britain.

This need not come at the expense of loyalty. The template was set by Blair and Brown during the 1980s and early 1990s. Then, Labour's emerging leaders supported figures such as Neil Kinnock, Roy Hattersley and John Smith with loyalty, but also with new ideas and energy.

They were resolute in their support but showed no fear in asking challenging questions about the party's values and its direction.

The biggest challenge for our generation is to address the shortcomings of the baby boom era. The boomers help to tear down rigid social structures, creating a society in which all of us enjoy hard-won rights and freedoms.

But the liberation of the individual has helped to create a self-centred culture of consumerism and instant gratification. Our task is to help rehabilitate notions of mutual obligation, from parenting and family life to the co-operative and the employee mutual movement.

Mandela's children

Economically, baby boomers have benefited from the proceeds of rising house prices and generous final-salary pension schemes. But this has left younger generations to shoulder huge financial burdens. The question for us is how to spread asset ownership more fairly across social classes and between generations.

Baby boomers witnessed great battles between state socialism and liberal capitalism. But the credit crunch and recession remind us that Thatcherism was far from "the end of history". Our mission is to imagine a more civilised capitalism, with responsible banking but also space for family time, fair pay and decent work.

Gen X should be in a strong position to address these challenges precisely because our political upbringing marks us out from the baby boomers. Where the baby boomers so often saw the world in light and dark, our upbringing has been more nuanced and less certain.

This is the generation that reached adulthood as the Berlin Wall came down. We are the children of Ronald Reagan and Margaret Thatcher, but also of Nelson Mandela and Lech Walesa.

Politically, because Generation Xers grew to political maturity in the Noughties, we have a more objective view of New Labour's shortfalls as well as its achievements. Often we are more wary of the tribal politics of the 1970s and 1980s, and therefore more receptive to working beyond traditional party lines. This speaks not just to a need for electoral reform, but also to the need to build a movement of the left that connects with allies and potential supporters outside our party.

In a more secular world, our generation must start forging a more moral discourse that gets beyond pledge-card politics and speaks to people's values and identities. Our job is to move beyond the technocratic language of "what works". It is to lead rather than follow public opinion on issues such as equality and climate change.

Such a challenge demands that we grasp the possibilities of many-to-many communication, understanding that the era of "command-and-control" political communication is over.

Earn your rights

David Cameron's Conservatives serve as a cautionary tale. Their sense of entitlement is barely concealed as they cross off the days to a general election. Yet every day their platform looks thinner.

Progressive Conservatism has given way to tax breaks for a wealthy few. Modern Conservatism has been stamped out by a return to "back-to-basics" family tax breaks. "Vote blue, go green" is laughable, given that Tory candidates rank climate change bottom of their list of priorities.

Whether the Tory leadership ever really believed these things does not really matter; what we should learn is that intellectual renewal is not easy and it takes courage.

For Labour's Gen X, this is a decisive moment and a unique opportunity to shape the political agenda for the next decade. We must seize the opportunity, or we will lose it. No individual or group has an inalienable right to our party's future.

Already, a younger generation of talented, committed campaigners is emerging. PPCs such as Chuka Umunna, Rachel Reeves and Stella Creasy will be huge assets to a party that may well decide to skip a generation.

The next generation of Labour leaders can no longer lean on the achievements of its predecessors or live in their shadow. Nor can we harbour what is often seen as a sense of entitlement. The right to govern must be earned and won.

We can no longer afford our politics to be bogged down in the minutiae of public-service reform or the finer points of the tax credit system. We need to start contributing to bigger questions about where the country is heading and what type of society we want to live in.

Gordon Brown, Peter Mandelson and Harriet Harman will all still be there after the election, but they have carried the rest of us for too long now.

David Lammy is the Labour MP for Tottenham and the higher education minister.