I really wouldn't worry about work experience until you're 18 and at university (at which point, I'd try and get a paid job which provides experience - though I wouldn't discourage you from doing voluntary work too). You will be highly unlikely to be cleared to work with people until you are 18 due to safeguarding concerns. We're due to get a volunteer here in the next month or so who is under 18, we're going to have a real problem finding meaningful work for them in which they do not even see patients details. The reality is that they will be doing glorified admin work (even the undergrad volunteer who is due to start is going to be typing numbers into a computer).
Volunteering with befriending services, Youth Offending Services, homeless charities, older adults homes, etc will provide far more practical experience that will actually teach you meaningful skills.
And as has been said, focusing on your wider reading at the stage adds more to your application.