Second Hand Mac Laptop - Rekordbox

Hi, Sorry for asking a silly question, but I have never had a Apple laptop before, I have always used Windows. I want to get a cheap second hand mac pro (13 inch) to use for home djing. I don't want to spend a lot of money and it will only be used for RekordBox, Itunes and Audacity (recording software).

RekordBox is the highest spec: I5/I7/I9 (2.4GH), 8mb ram and IOS 10.13/10.14/10.15 (all latest updates). I see a lot of older laptops on eBay for around £300, but will they work? I understand the CPU and ram, but confused about the IOS.....a lot of the cheaper ones state 10.13 (not updated to latest version), does that mean they can't be updated and wont work with the software.?

Thanks for any advice given, don't want to spend £1`,000 just for a bit of home mixing.

Thomas