When were our bones mostly cartilage?

During the embryonic stage, our skeletons are mostly made of cartilage. Cartilage is a flexible, connective tissue that helps to support and protect developing bones. As development progresses, the cartilage gradually calcifies and hardens into bone through a process called ossification. By the time an infant is born, their bones are mostly ossified, but cartilage continues to play a significant role in bone growth and remodeling throughout childhood and adolescence.