There is an element of ringfencing with the Winter Fuel Allowance, free TV licences and bus passes.
Old people vote. Young people don't. Therefore it is usually good tactically to please old people.
However there is also a more fundamental point. Should benefits be universal or means-tested?
Universal benefits are wasteful because they go to people who don't need them. By doing so they often lock into an annoying dependence on the State.
However means-tested benefits require oodles of admin, and more perniciously, increase effective marginal tax rates. If the benefits is purely paid for compassionate reasons, these questions don'really t arise - but especially for employment related benefits, means testing acts as an active disincentive to work.
The balance between means-testing and universality is very difficult.