Mark needed in MPhil to get funding for a PhD

I've applied for a PhD in economic and social history at Oxford. I guess quite a number of people get accepted but then don't get funding. So I'm wondering what the chances are. I got 84 for my MPhil dissertation at Cambridge, which gave me an overall aggregate of 81. I've heard of people with aggregates in the 70's getting funded. However, my marks at undergraduate weren't very good. Also, I'm 50 years old so wondering if that might go against me.

It isn't the mark that is the threshold, it's a matter of what funding is available. So the department may have access to funds that are just about academic merit, in which case each fund will say how its monies are to be disbursed. Some priorities full funding, ie one full fee scholarship will be awarded - in which case it will go to whoever gets the highest grades. The fund rules might say the money available that year to be shared equally across the top 3, candidates.
Other funds are about specific characteristics, so if there is a fund only for students over 50, you're in with a high chance, even if you scraped in by the skin of your teeth, ditto if there's an award for children of grocers from Nottingham, and you are one of those fortunate few (my College had that specific scholarship - I always wondered how often it was awarded).
Your age won't go against you, I won a full scholarship at about your age, albeit from the light blue side. With an 81% average from Cam, I should think you'd be a strong contender for any funding that was available.