Opinions On Baby's Age For BF

Hi, I've been watching Youtube on mothers' breastfeeding their baby, and came across a video of a mom breastfeeding her child which is a 6 years old girl. The oldest I heard was this mother still breastfeeding her Primary 1 kid. I know breast milk is healthy, but what are your opinions on how old your baby should stop breastfeeding and must drink from a cup or bottle instead?