If you are doing work different from that of an employee of the opposite sex in the same establishment, or at another establishment where common terms and conditions apply, but the different jobs have been 'rated as equivalent' under a job evaluation scheme, you are entitled to equal pay.
There has to be someone of the opposite sex in the same employment, with whom you can compare yourself (a 'comparator'). Differences such as payment for extra responsibilities are permitted, provided the differences are not related to the sex of the worker.
The law applies to all workers, regardless of age. If you think you have an equal pay claim, get further advice from, for example, your trade union if you have one.