What is the average age babies sit up?

While all babies progress through milestones at different paces, most babies sit on their own by seven months of age, according to Baby Center. It is considered a red flag if a child seven months old, or older, cannot sit unassisted.

Baby Center describes other milestones the average baby should reach by seven months old. These milestones include: babbling, grasping objects with a raking motion, and responding to their names by turning when called.

Certain red flags to watch for include: unresponsiveness to noises, an overly stiff or floppy body, and an inability to show affection to family. Parents should speak with a doctor if they notice any of these signs.