A not very common story but getting more common. This woman in the link supposedly got pregnant 'naturally' at 51/52, (not sure if its true or not, because it's seems a bit of a coincidence that she just happened to have a multiple birth which almost always happens with IVF,) but I guess it's certainly possible to have a natural conception in your early 50s. But is it too old to become a mother/parent? Here is the link to the story...
http://uk.lifestyle.yahoo.com/...ahoo-lifestyles.html