Infant Car Seat G2 (Model No. ORB823000 and/or ORB833000): can be used with children starting at 4 pounds and 19 inches, until they are 30 pounds or 32 inches long. The usage rating is by height and weight, not by age - children reach the maximum height or weight at various ages, ranging from about 6 to 18 months old.
Please note that some Orbit Baby Infant Car Seat G2s do not reflect this increased weight rating on their labels, see here for more information.
Generation-one Infant Car Seat (Model No. ORB803000): can be used with children up to 22 pounds, and up to 29 inches.