Around 6.5 months up - but you have to be patience as each baby is different. My baby can't sit properly on his 6.5 months, but now he can sit tight at his 7.5 months, but sometimes like a " 不倒翁" as baby takes time to develop their skeleton.
Especially when they sit with diapers, more difficult to keep themselves balance on a chair la!!
7 months. If your baby weighs less (lighter), he or she may be able to sit before 7 months. if heavier, may be 7 months or after. Babies are different ...