The ACAS report makes good reading. I'll dig out some case examples.

http://www.acas.org.uk/media/pdf/i/1/Age-and-the-Workplace-a...

Excerpt:

Avoid references, however oblique, to age in both the job description and the person specification. For example, avoid asking for ‘so many years’ experience. This may rule out younger people who have the skills required but have not had the opportunity to demonstrate them over an extended period. A jobseeker could challenge any time requirement and you may have to justify it in objective terms.