it's 2 years old and 40 lbs here. but my daughter is 4 and 30 lbs and has been front facing since she was around 1- 1/2. her poor legs was all folded up so we turned her around early it was making her legs hurt anytime we was in the car.

I think when the baby gets 1 but my kids are tall so they would be cramped up so I put them forward when they were 10/11 months

usually with most convertible car seats it goes up to 40 pounds rear facing...but check the manual. it is recommended to do rear facing for as long as possible...some state laws are 1 or 2 years of age but I plan on doing it for as long as possible past 2 years...it's just safer.

the determine that based on weight and age

I think it depends on weight