"The situation on the ground is getting worse and worse," she told Central Lobby.
"Local authorities are under strong financial pressure. We expect the government not to duck the difficult issue, not to go for incremental reform but go for radical reform as promised."
Ms Mitchell has worked for Age UK and before that Age Concern for nine years, and she warned that after years of consultation and the resulting Dilnot report, now is the time for politicians to reach for bold solutions.
"There is a danger that it will involve tinkering at the edges rather than the radical reform that the government has promised. If that is the case it would be a significant betrayal of many vulnerable people in society, including older people, disabled people and their carers," she said.
"I am passionately committed to poverty and social justice issues and there are major challenges for older people including discrimination, poor outcomes and extremely poor care."
The challenge of social care is huge - there are 2 million older people in England with care-related needs and nearly 800,000 people are unable to get any formal support for care. At the same time spending on social care has been cut by 4.5% in the past year and 80% of local authorities have restricted care to those with critical or substantial need, leaving hundreds of thousands to miss out.
The Dilnot commission has proposed that people should pay for the first £35,000 of their care needs. It said that would "pool the risk, take the fear away and also create a space where the financial services sector could start to be active".
Ms Mitchell said the while the £35,000 cap has gained lots of headlines, it is just "one fundamental element of the overall package of reform because what Dilnot proposes".
"We think it would be able to stimulate the private sector and the insurance market. Dilnot also recommended a whole range of things such as changing the law to make it clear what entitlement you have, better information and advice and being able to take your care from area to area.
"He also talked about the chronic underfunding of social care. At the minute the investment has not kept up with demand, with the numbers of older people and disabled adults requiring care. Local authorities are making it much harder for people to get the care they need and the costs of care are going up significantly more than inflation."
Age UK is involved not just in issues of social care.
"Our philosophy is we are fundamentally driven by our charitable mission and that includes tacking poverty, ill-health isolation, loneliness and improving care." Ms Mitchell said.
"But to be effective, and do more, we try and build broad coalitions of support. We work with the public, private and voluntary sectors and with those who share our values to increase our reach.
"We have also invested in providing commercial products targeted at the 50-plus market, primarily because that money enables us to provide more charitable activity and allows us to continue to expand at a time when many organisations are facing cuts. We provide products that meet the needs of people in later life."
While older people are living longer, for some
"I am predicted to live much longer than my mother or grandmother which is a huge cause for celebration," Ms Mitchell said.
"For many people retirement is a time of opportunity, people talk about it very positively as a time when they continue to make a contribution, supporting their families with child care or volunteering themselves or caring for their siblings, but it can also be a time of pressure and difficulty for others."
Many older people are affected by negative stereotypes in the media.
In last month's Budget, George Osborne referred to the "burden" of elderly people. Ms Mitchell said that this sort of attitude must be challenged.
"We haven't changed the media or the public debate about older people. Particularly in political media they are described in deficit terms. What I mean by that is the burden of aging. The 'greedy geezers', the 'baby boomers', often portrayed as being victims, who are bleeding the country dry of money for younger people.
"We absolutely believe at any point in your life, the quality of life is critical. Right up to the day you die you have a contribution to make and many, many older people continue to make hugely important contributions, including working beyond the age of retirement and volunteering. There are millions of older carers supporting siblings and their husbands and wives at time when much of the care is being cut.
"We want to see a huge shift in the media and in the public debate. It does have an impact. We constantly see images of older people as victims who are weak. It portrays a poor image of old people and that impacts on how they feel, how they think and how they perceive their own abilities.
"Ageism comes in many forms from serious human rights abuses which we have seen catalogued recently in care homes and hospitals where the treatment is appalling right through to patronising language and all of that ties together to have a negative impact."
Ms Mitchell said politicians should remember that older people know how to make their voice heard at the ballot box.
"Not only are they growing in number, they are much more likely to turn out to vote and they are less likely to swing. So once you have got them, they are much more likely to stick with you."