"While 70.9 percent of mothers in US hospitals initiated breastfeeding in 2003, only 36.2 percent were still partially breastfeeding at six months of age and only 14.2 percent were exclusively breastfeeding at this age. The American Academy of Pediatrics states that exclusive breastfeeding is the ideal nutrition for the first 6 months and should continue for at least twelve months and thereafter for as long as mutually desired."
I think my daughter was still breastfeeding just at night to go to sleep when she was three. With my encouragement, she stopped when she had her 4th birthday. (sort of a "big girl" thing, I think I spun it as. If truly "child-led" it would have gone on even longer, I think.) I think if the mother is feeling fed up with it, that is a reason to encourage weaning or limiting breast feeding -- at least after the first 12 months or so.
www.lalecheleague.org