WizofOz
"It doesn't work that way. Employers can set any criteria they want"
Errr, no they can't actually. Certainly not in the EU anyhow.
It is totally illegal to mention age or sex, sexual orientation, ethnicity, religion or disability in any job advert.
That isn't to say that discrimination can take place during the subsequent stages of a process due to any number of factors which may be difficult to prove.
Positive discrimination CAN be used when selecting someone for a role, such as this: You have an office role which is suited to people of any age. However, you have a majority of young staff in place. Therefore, a 66 year female may well be an equally good candidate compared to a 23 year old graduate. As an employer you CAN offer the job with a reasoning such as "she will give us a slightly different demographic fit".
But, that is of course different to advertising for positions which require certain skill sets - such as 500 hours on type. This IS legal and as you say can and is used.