Different formula stages?

Ma

My son is 7 months and the formula we’re using says to use stage 1 until 6 months then switch to stage 2 until around 10 months, then use stage 3. I’ve also read that I can leave him on stage 1 for his whole first year.

So what am I supposed to do? I’m leaving him on stage 1 for now and he seems fine, but I wonder if I should switch? We’re also giving him solids twice a day, but he doesn’t eat much at each solid meal.