While each model varies just a bit (often depending on whether or not the model is compatible with a car seat), but generally speaking, children can be sat comfortably and safely in the jogging stroller anywhere from around 6 months to 5 years old.
However, the child must be able to hold their head up without any help. We also recommend the children be at least 12 months old before jogging on trails, grass, gravel, or any other kind of potentially uneven terrain.