Yes. Under the Equality Act 2010, harassment is defined as any unwanted conduct that violates your dignity or creates an intimidating, hostile, degrading, humiliating or offensive environment for you. So, for example, if a colleague repeatedly taunts you with age-related insults, you would have a claim against them and your employer, which could include damages for injury to feelings.
Equally, young workers may have a claim where they have been subjected to degrading workplace 'initiation rites'. Conduct will not be unlawful if in all the circumstances it would not be reasonable to view it as harassment. But your view as the complainant must be given particular weight in any assessment of what is, or is not, harassment.
You are also protected if someone, such as a recruiter, mistakenly assumes you are older or younger than you actually are, and treats you less favourably as a result.