From what I gather there where 65+ yr olds in the trials, but not enough to be able to say with statistical certainty how well it worked.
However those that where in the study all mounted a robust response & no bad outcomes. Thus UK mhra said on balance it should work in 65+ (educated guess with some evidence). Where as EU country regulators took the lack of statistical definitive evidence to say not to be used in over 65s.
And now we have millions of 65+ having had the AZ vaccine, the data now confirms it's a very effective vaccine (75%+ with just one jab).
But the negative message in Europe is now ingrained and that is a hard thing to undo. Maybe a rebrand?
Also AZ one benefits with 8+ week gap between both doses as it makes it more effective.
Ps: I also suspect some politics in the not to be used in over 65s, as there was massive supply shortage of AZ for EU and perhaps it was a way of reducing initial demand and saving face.
The EU did get a better price for all their vaccines & making the companies liable for any issues people had with the vaccines, but at cost of time.
UK underwrote that to expedite things. (Goes to show if you hire people who work in pharma companies to get vaccine purchases done fast, they know the shortcuts. - UK vaccine task force)