Old beer is not harmful to health. The EU requirement to place a consume-by date on the bottles was introduced a couple of years ago.
The Objective Beer Tasters, a Belgian association of beer consumers, conducted a campaign against this measure in the past. The breweries are not happy with a compulsory consume-by date on the label, either. Beer does not really go off, although the flavour can change and it may turn slightly cloudy.

Lager in particular has a tendency to cloud over time. The gradual clouding is caused by bonds being formed between proteins (from the malt) and polyphenols (from the chaff of the malt and the hops), so that is why types of malt are selected with not too high a protein content in which the proteins easily coagulate and can be removed during the brewing process. Consumers do not like cloudy lager. Keeping lager clear is generally a sales issue. Drinking cloudy lager has no effect on the health of the drinker. Some special beers are deliberately made and sold cloudy.