Companies continuing to discriminate against older staff will put themselves at a competitive disadvantage in the future, according to IT industry body Intellect.
New employment laws come into force on 1 October when it will become illegal for companies to deny a job or promotion to anyone because of their age, while job adverts will not be able to call for "young" or "enthusiastic" workers or specify a minimum number of years' experience.
Beatrice Rogers, senior programme manager for the knowledge economy at Intellect, said ageism is not endemic across the IT industry but that it is an issue.
She told ZDNet UK's sister site, silicon.com: "It is ageism against young people coming into the industry and ageism against the older people not seen to be as dynamic or useful."
But she warned that companies continuing to discriminate against workers on grounds of age are missing a trick as the UK faces an IT skills shortage.
Rogers said: "One of the factors the EU and UK have to face is that we are becoming an ageing population. If you continue to discriminate against older people you will have a much smaller pool of resources to tap into. In today's society business cannot afford to be ageist."
Graham Benson, IT director of the Web Factory, the IT services arm of online retailer Play.com, said a high-performance team requires a mixture of competence, experience and capability.
He told silicon.com: "It is imperative that we continue to balance the raw enthusiasm and commitment of youth with the greater level of experience and expertise often held by those that have 'been around the block' a few times."
Employment arbitration body Acas warned that almost a quarter of companies currently specify maximum recruitment ages and many also use age to fix a starting salary.
Rita Donaghy, chair of Acas, said: "Organisations need to be aware of the changes they need to make so that they don't discriminate and miss out on valuable skills."
But Intellect's Rogers also warned that the Government is offering little incentive, particularly to small and medium-sized businesses, for companies to invest in lifelong learning and training.
She said: "Lifelong learning is going to be increasingly important and we are going to continue to need to develop skills throughout our life. But it's very difficult for businesses to claim any training against tax. There is no incentive to invest in skills."