I am 38 and was unemployed for a few months so took the job as I was desperate. Your contract will be 16 or 20 hours a week. Full time vacancies are for supervisors or managers only. There is usually plenty of overtime if you want it. I was on the fill shift which is basically a shelf stacker. It can be strenuous work but that wasn't the issue. The main problems for me were sitting in a cramped staff room with a bunch of immature staff members shouting and swearing at eachother. You are expected to wait for the delivery to arrive. You are not paid for waiting. On my first day I started at 8 and the delivery didn't arrive until 11. I went home and came back. A few days later the delivery hadn't arrived by 9.30am. No manager came to tell us what was happening. After sitting in a kindergarten staff room for an hour and a half I walked out. The problem was my age. If you're young you may enjoy the job.
When you are put on the till from time to time you have to shout for your colleagues to call your manager if there are any issues. There is no other way of contacting them. I thought this was very unprofessional.