giving birth at 55 would not just be unusual but miraculous - it is possible with today's modern fertility treatment to bear a child in mid 50's but only via artificial means.
I would like any record of a conception on Island to a woman aged 44 or over (ie birth age 45) - there is a detailed study on late births in England from Parish regs which I have quoted from before but don't have access to book at present til I return to UK but such births post 45 are exceedingly rare.
My own view is that any such apparent births in the records are the mother hiding an illegitimate birth by a young daughter (or as for Mrs Hall Caine fathered by a wayward son)