at 16 you can do work experience or volunteering in most places, but there may be a few limits (e.g. you won't be able to do volunteering involving personal care, or work experience in observing practical procedures/surgery). Other than that, just look up some hospitals or care homes near you and see if there's anything you'd like to apply for. Keep in mind that you may want to leave volunteer applications until summer if you want to focus on your gcses right now instead of a 'job', but the sooner the better in terms of applying for short term work exp programmes.