“Nans against Nazis” read one large placard brandished at the recent anti-racism protests in Liverpool. It belonged to 71-year-old Pat. “Someone said to me, ‘You’re too old, don’t be doing this,’” she told the Independent. “But as long as they’re here someone’s got to do it.” She’s not the only one who refuses to be invisible. As the editor of BBC Radio 4’s Woman’s Hour for more than a decade, I became so familiar with countless stories of active, busy older women that I’ve now written a book of advice for today’s grandmothers.

I interviewed more than 100 women. Many of them were exasperated at the tired old stereotypes that either portray us as frail, ancient, hobbling, lonely old biddies, or the equally cliched antithesis: “battling grannies” or “granny heroines”. The very word “granny” has become a shorthand for “old lady”, a handy way to define us by our age and dwindling status (and it bears little relation to whether or not you actually have grandchildren).

It’s still glibly assumed that, once a woman becomes a grandmother, everything else in her life becomes irrelevant. That’s absurdly outdated.Whatever their age, many grandmothers will continue working or will lead busy, demanding lives outside their family responsibilities. The deputy prime minister, Angela Rayner, who at 44 is the youngest grandmother in parliament, doesn’t appear to see any conflict between the two roles.

Despite this, some clearly find the traditional image so ludicrous that they turn to parody. “I’m going to be a little bit more of a granny,” Joanna Lumley told the Northern Echo. “Which involves eating a lot of cake and becoming quite big. I want to have one of those housecoat overalls, a nice big one so I get a bit Demis Roussos about it.” I remember the comedian Jenny Eclair saying: “I want to be a good nana, but I’m not sure what this entails. I think it means putting protective sheeting over the good sofa, blockading the stairs and trying not to mind when they bring a truckload of plastic toys with them – what’s wrong with a simple wooden spinning top?”

According to Age UK, 40% of the country’s grandparents over the age of 50 have regularly looked after their grandchildren. But that pattern is beginning to change. The forum Gransnet teems with grandmothers who are tired of entitled offspring who expect free childcare on tap. “We often have to reschedule work commitments to fit in with grandkids’ needs, and cancel social invitations,” writes one disgruntled granny. Many grandmothers lead busy, active lives and aren’t ready to regard themselves simply as childminders. Many of those I spoke to for my book resented any suggestion that older means duller, more passive or more conservative.

This growing backlash is personified by Raging Grannies, a group of activists who campaign across North America on peace and environmental causes, challenging stereotypical views of older women and the assumption that political action is only for the young. During more than 30 years of activism, Raging Grannies have held several anti-war rallies, and in July 2005 five members of the group were charged with trespassing after they attempted to enlist at a US army recruitment centre in Tucson, Arizona. The group said they wanted to be sent to Iraq so that their children and grandchildren could come home.

They represent many grandmothers across the world who are working to make a difference. Frequently, these women are drawn to campaigning by their concern for the environment. This year, a group of older women in Switzerland won the first climate change victory in the European court of human rights, claiming that their country’s inaction on fossil fuels violated their human rights. The group of more than 2,000 women, known as the “climate grannies”, argued that because older women are more likely to die in heatwaves – which have become hotter and more common because of fossil fuels – Switzerland should do its share to stop the planet heating, and to abide by the Paris agreement target of 1.5C. The ruling demonstrated the power of older women. “We are not made to sit in a rocking chair and knit,” said one of their members, Elizabeth Stern.

They aren’t alone. Take the International Council of Thirteen Indigenous Grandmothers, whose participants range from the Arctic to Brazil, Tibet to Mexico. Their faith is based on spiritual principles and the practice of traditional medicines. They’re deeply concerned with environmental degradation, poverty, our materialist culture and the destruction of indigenous ways of life. Crucially, they believe that the wisdom of our ancestors can “light our way through an uncertain future”.

Other groups were founded to cope with specific challenges. The Grandmothers to Grandmothers Campaign, a cross-continental project formed in 2006, was set up in response to the crisis faced by grandmothers in African countries as they struggled to raise millions of children orphaned by Aids. The project originally brought together African and Canadian women to support and learn from each other, raising funds and creating educational programmes to support them.

The project has since raised more than $40m, and now includes grandmother groups in Canada, Australia, the UK and the US. Their work is highlighted by the US photojournalist Paola Gianturco, whose book Grandmother Power: A Global Phenomenon assembles an inspiring gallery of women determined to make a difference. Among her subjects are Indian grandmothers bringing solar energy and light to their villages, and Argentinian grandmothers who have searched out and returned more than 100 children kidnapped during the military dictatorship of the late 1970s.

You may not be mounting the barricades, shouting out on Instagram, organising food boycotts or suing your country, but by doing what you can to make the world better for the next generation, and filling your life (and those of your grandchildren, if you have them) with love, goodness and a commitment to ethical principles, you can still be a raging granny. Dismiss us at your peril.