I think it's fair to say that Cambridge are more explicitly concentrated on catering to mature students than Oxford are. Cambridge has 3 colleges exclusively for mature students, Hughes Hall (approx 200 undergraduates), St Edmund's (also approx 200 undergraduates), and Wolfson (187 undergraduates). Oxford has just Harris Manchester, with just 92 undergraduates, less than half of any of Cambridge's. Oxford's way might actually be preferable if mature students were more frequently scattered through all the other colleges as equal-feeling members than they are at Cambridge. However I have no evidence this is the case as Cambridge say that 3% of their students are mature (21+) but I can't find any stat for Oxford. So my feeling is that Cambridge might be easier to get in to for a mature student than getting in to Oxford. Cambridge is known for being a little more left-wing so it possibly makes sense (to Oxford anyway) that Oxford would be harsher on someone who might have taken ages to get themselves in sufficient gear when they could be offering a place to more 18 year olds who usually only have one attempt at getting in university.