Walk into the lobby of any of the big accountancy firms and you could be forgiven for thinking you had accidentally stumbled into the 1976 science fiction movie, Logan's Run.

The movie, which is based on a novel of the same name by American authors William F Nolan and George Clayton Johnson, portrays a futuristic world where overpopulation is controlled by killing everyone over the age of 30.

It's not the sort of personnel strategy the accountancy profession would ever consider, but in contrast to their fusty stereotype, accountancy firms often have a thriving youth culture and annually recruit large swathes of staff fresh from university.

All this could change with the introduction of the Age Discrimination Act, which forbids employers from practising unjust direct and indirect age discrimination against employees of all ages.

The new act, arguably the most far-reaching piece of employment legislation since the Sex Discrimination and Race Relations Acts some 30-odd years ago, could potentially open up the profession to people of all ages who want to train as an accountant later in life and bring a new lease of 'career life' for the sizeable pool of accountants in their 50s who have traditionally struggled to find work.

Under the new legislation, firms can no longer rely solely on the university milk round to recruit new trainees and will instead have to adjust their recruitment practices to appeal to people at varied stages in life.

Use of the words 'young', 'old', 'mature', 'energetic' and even 'graduate' in recruitment ads will be no-nos, as will recruiting trainees exclusively from holiday vacation schemes that favour students on breaks between university terms.

But although the introduction of the act has prompted firms to review their recruitment procedures, it has not caused widespread panic.

At Ernst & Young, where the average age of staff members is 32, the upper age limit for the graduate training scheme was abandoned some years ago in recognition of changing social demographics and trends such as people travelling after university. Its oldest trainee in recent years was aged 37.

E&Y, which has spent the past year preparing for the introduction of the new act, both expects and welcomes applications to its training scheme from people aged 30-plus who are looking to make a mid-life career change.

'We're looking for the best people, whatever their age is,' says Paul Quinlan, senior manager, employee relations. 'Like many large recruiters, we're struggling to get the people we want and we're fishing in a smaller and smaller pool.'

It's a dilemma shared by mid-tier firm PKF, which takes on about 65-70 trainees each year. This year the firm's oldest trainee is 31 and its youngest is 20, although human resources director Kevin Dickinson expects this age band to widen with the new legislation.

Nevertheless, he points out that in the past hiring older candidates has presented cultural issues in terms of trainees reporting to people significantly younger and managers supervising people significantly older than themselves, but insists it's difficult to generalise.

'Sometimes it was a problem, sometimes it wasn't,' he says. 'Some mature people are better applied at studying, but because they are out of the studying loop, others find it difficult to get back in.' He believes the issue for firms will be handling trainee applications from candidates in their mid-50s since employers want to get sufficient payback for the investment they make in training new staff.

But Richard Smith, employment director for HR consultancy Croner, argues that hiring older candidates might actually prove cost-effective for firms.

'One of the great problems for accountancy practices is that having trained people, they can't hold on to them,' he says. 'You're more likely to get 10 years' service out of the 55-year-old than you are out of the 25-year-old.'

Hiring trainees is not the only potential legal minefield. Taking on experienced hires has also become a quagmire, since employers can no longer specify a certain number of years' post-qualification experience in job ads. 'Post-qualification experience is indirectly discriminatory to younger people,' says Richard Martin, a partner and employment law specialist with City law firm Speechly Bircham. 'If you specify six years PQE, no one under 28 can meet it.'

He says employers will now have to recruit according to the skills they're looking for, instead of relying on PQE as 'lazy shorthand' to find staff of the approximate skill level they require.

Meanwhile, firms that have long working-hours cultures will need to take a good, hard look at themselves. Martin says there's a risk that firms that do not adjust their practices to allow people with families to work for them may be indirectly breaching the age discrimination legislation.

For a long time many accountancy firms had an 'up or out' culture where staff either kept climbing the corporate ladder or were forced to get off it. This has changed in recent years as firms realised they were losing valuable skills by not allowing staff to move sideways. The new legislation should bolster the cultural shift.

But is there a risk that firms could get 'clogged up' by keeping the staff they would previously have urged to move on? And will their ability to offer rapid career progression to talented newcomers be affected?

Ernst & Young acknowledges the difficulty. 'There is still going to be that pressure to make room for new joiners to go upwards and the firm will have to keep expanding and growing to accommodate them,' says Quinlan.

Croner's Richard Smith believes the problem, which seems significant in theory, will work itself out in practice. 'People move around anyway,' he says.

But while the Age Discrimination Act could open up a world of opportunities to both aspiring and experienced accountants in their 50s, not everyone is convinced it is going to dramatically improve the lot of those labouring under the depressing moniker of 'pale, stale males'.

Martin Lloyd-Penny, ex BDO partner and founder of specialist recruitment agency matureaccountants.com, points out that in a profession it is important to stay technically up-to-date and unless they get up-to-date, many older accountants would not be considered for the same positions as newly qualifieds, even if they wanted to do them.

And although he agrees there's nothing to stop people re-training later in life, Lloyd-Penny doesn't expect to see an influx of mature, would-be accountants. There is stiff competition for the best graduates, but the big accountancy firms still have extremely vigorous selection processes, he says. 'If they're being that selective with young people, it would be harder for someone in their 40s or 50s.'

Without doubt the Age Discrimination Act has huge cultural implications for our society, not least because we are brought up to respect our elders rather than to manage them.

Businesses will need to re-educate their staff and lawyers are predicting a litigation boom from so-called 'ambulance chasers' pursuing discrimination claims against organisations with poor processes.

It is unlikely that there will be an overnight change in the demographics of the accountancy profession and that the hordes of youngsters who oil its cogs will vanish overnight. But change will happen, gradually, and given our ageing population - by 2021, 40% of the UK population will be over 50 - it seems in the best interests of the accountancy profession that it does.