Hi, sorry for the late reply, I hope you get this message.
Well, I’m no doctor and I’m not a geneticist but I’ll hazard a guess! I suspect it is a combination of various factors and genetics probably plays a large part in that. I also wonder whether it is due to their quality of life, i.e. access to good food, healthcare, etc.
I’m inclined to also say that it might be due to the job that the royal family do, but using the Queen as an example contradicts that theory because she worked really hard, including during the war, and also had four children! As a mum of two I can vouch that having children is hard work!
My great auntie lived to 104 so perhaps it’s a female disposition… If you find out the answer, let me know!