Is there an age limit to who you would ask to care for your children? E.g your 70/80 year old parents?

I don't know that I would put an upper age limit who I would let take care of my child. Instead I would put an ability limit. If they are able to do the basics for child care and keep up with my daughter, and I trusted them, then I would let them. If they were unable, I would have someone else take care of my child, but still let the other "help."