I was surprised the other day in Sarah's post to find when they took her dad on holiday it was for his 50th, so he's no more than mid 50s now. Assuming her mum would have been a similar age too, nana is likely no older than mid 70s. She seems to have a few health problems - unable to walk far and needing wheelchair or mobility scooter to get about, some kind of dementia as they were so worried about her when she went missing. But she has been seen walking fine around the white rose when no mobility scooter is available, and who was looking after her before she went to Portugal? Sarah was away and Katrina was isolating. Sarah makes out there's only really her to look after nana.
Did Sarah's dad ever work? He appears to have been "retired" from a young age, and I can't imagine he had such a good job he managed to save up enough to fund an early retirement.
With health problems affecting the family younger than you would expect then you'd think Sarah would be even more conscious of keeping healthy, yet doesn't seem concerned that she's out of breath after a short walk across the camp site.