J.S.
He can sit comfortably rear-facing for the entire ride. I kept my children rear-facing until they were three years old even though the recommendations are for five years old.
EDIT: Child car seat safety advocates routinely endorse keeping children in rear-facing car safety seats for as long as possible. They recommend until at least 5 years old, and some people who are die-hard about it even keep their children rear-facing until 7 years old. There are convertible booster seats that allow this, so it's entirely possible. You can find this stuff out easily on car seat safety web sites and even YouTube.
It's not law, but recommended strongly.