Bit conflicting with the person above, but I think first person is fine. There's not really another way to say a lot of things. I've written in first person for all my CVs that got me jobs.
Your CV looks fine, it is a bit wordy and can be significantly cut down in places, which might make employers overlook some important detail because they can't be bothered to read it all. Do you have any other experience from school you can add (even voluntary, like e.g. a school prefect or sports team captain that you can add under 'other positions of responsibility' or similar?) which would help bulk it out?
My main recommendation would be to write a different personal statement for each role you apply to - e.g. emphasise if your previous sales assistant role is in a sector very relevant to a job you're applying, say why you want to work for certain companies. Emphasise your experience in customer service and communication with different groups of people in your personal statement which you don't really do at the moment, but that will be the key thing they're looking for.