[Rosie] When I was at school, there was a boy there whose father was in his 80s. (I know it sounds like one of those silly school rumours, but you'll have to trust me that this one was true. Apparently the dad had plenty of money and the rest is history.)
[Rosie] Yep, your maths is right. It will perhaps ease your incredulity if I note that my grandmother was much younger than my grandfather (to the tune of just under fifty years, b. 1917).