pls explain the struldbrugs

Struldbrugs are creatures which inhabit Luggnagg. They are characterised by a red dot above their left eyebrow. They live as normal species till they are thirty years old but soon they become dejected and start ageing. However, they are immortal and due to the rapid ageing process (which causes blindness and loss of hair) they are legally considered dead at the age of eighty. Beyond this age, they are not allowed to hold property or take part in any civil procedures.