Age refers to a person belonging to a particular age group, which can include people of the same age and people of a particular range of age.
The law protects people of all ages. You could be unlawfully discriminated against because you are 15 or because you are 85. In terms of employment, age is the only protected characteristic that allows an employer to justify direct or indirect discrimination. An employer may be able to justify (in)direct discrimination if they can show that their actions were a proportionate means of meeting a legitimate aim. This means that different treatment can be justifiable if there is objective evidence to support the decision. A common example used to be a compulsory retirement age.