Is it weird that someone should breastfeed their kid at age 5?

That's disgusting. Tops should be a year old.

Wish I could milk my stepmoms breast. Mmmmmmmm

I consider it weird.  Most women stop breastfeeding sometime between one year to two years old.

There is no reason that a child past the age of one year old would actually NEED breast milk.  By the age of one, the average baby is eating enough solid foods to transition to cows milk or some other form of milk if there is a lactose issue.  

I’ve known mothers who nursed their kids until maybe age 3, but 5 seems too old. A child shouldn’t still be nursing when they start school. I don’t think kids should be nursing when they’re old enough to remember it later on. 

A 5 year old doesn't need to be breast fed anymore, very strange. 

Yes.  I raised three children, breast fed each but stopped at 1-year of age.

dad must be PRETTY LONELY by now. And no it is not correct at all- your sister needs some counseling and maybe/probably the child too in a few more years.