My son was diagnosed with ADHD at 6 (mild ADD, heavy H!), but not put on medication unless/until he started 'getting in his own way' at school. As in, when it was clear his ADHD symptoms were causing him to distract himself from his own learning, i.e. continually skim/skip over step 2 and 3 in a four step math problem, or rush/skip over entire instructions on a test, etc., causing his As and Bs to drop. So my son was probably 9 or 10 before we started medication. And I wouldn't say it made him all that much less hyper, but it helped him to not be restless/squirmy, and really helped him be more focused in school when he needed to be. He still had to work really hard at the not blurting out answers thing. (You're kind of missing a 'filter' with ADD/ADHD)
I truly don't know what's common, but I think straight to medication at under age six for ADHD isn't common ... unless you're talking about some severe symptoms/issues, or at the very least, symptoms far more severe than I've seen in my own 'hyper' son.
HTH :seeya:
ETA: Most kids start kindergarten at 5 or 6. It's not usually obvious a child has ADD/ADHD until they are in school and have to sit still and focus and be quiet for long stretches of time--longer than they're usually expected to at home or at preschool. So for a parent/caregiver to notice super obvious 'hyperactivity' or an attention deficit beyond just being a happy/excitable/distracted kid....well, I just think if you noticed something that you and your doctor though required medication before age 6, it would have to be pretty severe symptoms. MOO!