The protections contained in the Equality Act 2010 apply to all job applicants and workers, including agency and contract workers, office holders (e.g. public appointees), the police, barristers and members of the armed forces. So whether or not you are described as an ‘employee’ or have a written contract of employment, you are likely to be covered if you apply for or carry out paid work for someone else.
Genuine volunteers are not protected against workplace age discrimination.
You may also challenge age discrimination against you by a university, college or a training provider or a qualification body or trade association (including a trade union). Providing courses that are only open to those under 25, for example, may be unlawful age discrimination unless the course provider can provide a good reason for the age restriction that will stand up to legal testing.