Car seat question: when are/did you switch to forward facing?

My son isn't going to outgrow the seat for a long time (40lbs for rear facing)--he'll probably be 7 years old! And the seat will expire before he's 6.

I'm starting to think that I will go straight from rear facing to a booster seat instead of switching the seat around.

When would you switch, even if the seat cold hold him/her rear facing till adulthood?

ETA when can you use a booster instead of a forward facing seat?