The world is undergoing a demographic revolution. We are witnessing the dividends of improving healthcare and living standards in rising longevity across the globe.

The number of people over the age of 60 is expected to increase (pdf) to 2 billion by 2050, from about 600 million in 2000. This change will be most dramatic in countries in the global south, where the number of older people is expected to triple during the next 40 years.

But, as often happens with demographic change, social attitudes and legal protection lag behind. Policymakers are left scrambling to keep up with the transforming landscape.

As the global population ages, there is an urgent need to reassess what role individual societies give to older people to ensure they are able to enjoy a decent standard of living and can continue to contribute to society as long as they wish. Shunting older people to the sidelines of our communities is not only unjust, it makes little sense for countries to miss out on the huge opportunities that longer life brings, and the asset that older people represent. Many older people continue working and also pass on important knowledge and skills to younger generations, and others act as carers to their family – in sub-Saharan Africa, 40% of Aids orphans are looked after by their grandparents.

Ageism is prominent around the world. In most countries it is still considered acceptable to deny people work, access to healthcare, education or the right to participate in government purely because of their age.

Indeed, apart from one exception (in relation to migrant workers and their families), international human rights conventions do not recognise specifically that age discrimination should not be allowed.

Human rights are, of course, universal, and thus older people's rights are protected in a general sense by the Universal Declaration of Human Rights, but the absence of an explicit mandate against age discrimination allows the issue to slip under the net and continue as acceptable practice.

Age International is therefore pushing for progress towards a new UN convention on the rights of older people, to clarify how rights can work better for people in later life. In August, governments will gather in New York to discuss how to strengthen the protection of human rights for older people as part of the UN open-ended working group on ageing. Aspart of the Global Alliance for the Rights of Older People and the HelpAge global network, Age International will call for governments to make formal proposals.

We have learned from the experience of human rights conventions for children, women and people with disabilities, that giving governments greater guidance on how to protect the rights of people in specific circumstances can have a huge impact on their wellbeing.

What it means to be "human" and to live with dignity, respect and security requires different responses from society, depending on our age and physical circumstances. This is widely accepted for other demographic groups, and should be the basis for our approach to older people. Older people are not a homogenous group – differences in how we age, our economic status and social standing underline the arbitrary nature of age discrimination. It is as baseless as race or gender discrimination.

In many countries the debate about how to adapt to a changing demographic has been framed in terms of how working-age people will cope with the "burden" of an ageing population, rather than recognising the value and potential older people bring to their communities when they live healthier, longer, active lives.

Experience shows us that if discrimination is made legally unacceptable, impetus is given to a societal shift in attitude – witness, for example, the transformation of women's lives in some countries where sex discrimination laws have been passed.

The need to make older people's rights clearer in law is increasingly important in many developing countries, where the impact of HIV, conflict and parents seeking work in cities have often meant grandparents are taking on the care of their grandchildren at a time in their lives when they most need support.

So, by enshrining older people's rights in a UN convention, not only would we ensure that we all have the best chance of enjoying security and dignity into old age, but that those caring for the next generation are given the best possible environment to raise happy, healthy, productive future adults.

Governments need to tackle these issues head on and make sure that global human rights legislation is fit for the future and able to respond to the opportunities and challenges of ageing in the 21st century.

• Chris Roles is director of Age International

Article from Guardian