JKR *hasn't* potentially broken canon at all. People *assumed* McGonagall's age based on only the information we had, but whoever said that was complete? Nobody.
The fact that she's always referred to as being elderly in the books "could have killed her *at her age*" etc suggests 50/60 was too young an estimate in the first place. You wouldn't refer to someone in their 50s or 60s as being frail even by muggle standards, because it's relatively young. Let alone in the wizarding world, where life expectancy is a good 30-40 years more.
As for Aurelius, Grindelwald is either lying about him being a Dumbledore or lying about their specific relationship.