I did at 15 months as my kids hated rear facing but now you can do extended rear facing which is safer.

I think it is actually recommended to have them rear facing until 2 years old. There should also be a guide on it in the instructions for the seat itself.

We only changed ours this month and she is turning two. Our seat allows for up to 36months rear, the longer the better for their safety

It depends of the height of your baby and the guide line instructions with the baby seat. A lot of babies hate facing backwards and will cry / scream for at least part of the trip. Facing backwards you also can’t see your baby properly unless you attach a special mirror to the baby seat and on sunny days your baby might get upset from the glare from it. You baby may be more prone to being sick or feeling nauseous while rear facing too. Bear in mind that if you put it on the driver’s side you may have trouble seeing properly in your rear vision mirror. That is definitely the case with booster seats. I know a tall driver who even when he lifts himself to above the seat he still can’t see properly in his mirror.

It was about six-seven months when I changed it. You probably can now.

There should be a marker on the chair to say

I think you have to wait until their shoulders reach the markers or anytime from 6 months old. I’m not sure if the laws are different depending on where you live. I changed my girls to forward facing at 6 months old, they were both tall enough and HATED being rear facing.

We didn’t change our daughter till she was about 1 and a half and her shoulders had reached the markers in her rear facing car seat