Being the youngest on the shift doesn’t make you the least important. The register doesn’t care how old you are.

Work is one of the few places where age stops being the main fact about you. The shelves get stocked or they do not, the customers get served or they do not, and reliability is visible whoever is sixteen and whoever is forty. That comes as a genuine relief after years of school sorting everybody by year group.

Be exactly on time, learn the parts nobody has shown you yet, and do the job without needing to be chased. Ask your questions early rather than guessing. Within a few weeks the older staff will treat you as a colleague, because what counts there is whether the work gets done.