As a former Admissions Tutor and current Head of Department, I'd second creamtea's advice. Think about why you want to study that specific course. But please, please, please DON'T talk about your "passion" for the subject ...
Think about what life skills you would bring to the course. Try to go through a few drafts do that you move from the personal, to the analytical.
Think about how these life skills would help you adjust to the rigours of study of the subject, and what you could bring to the course.
Show you know what is generally in the course, to show you've done your research.
As someone who's returning to study, your statement will give an indication of how well you can write, so make sure your grammar, spelling, and punctuation are error-free. Get someone with an eagle eye to proof read for you. Think about the logical structure of your statement, as this will show that you are capable of putting together a rational, reasoned argument (ie preparation for writing essays and reports).
And don't try to second guess the Admissions Tutor - yes, we will have read SOME of what you write in all the other statements, but that's OK. We're used to that. Make sure you include specifics about YOU - that's what we look for. And that you know what the course entails. We want a good fit both ways -- that you feel it's the right course for you, and that we feel that you will prosper in the course. We really don't set people up NOT to succeed!
Good luck -- it's great to see people returning to study. Generally, tutors love "mature age" students, because they're motivated and responsible and usually very very bright.