Also senior at the U.S. level =/= senior at the international level. The requirements to pass the senior free skate test is REALLY low, so that's why you have a lot of folks who compete at the senior level nationally but yet remain on the junior circuit internationally. Age limits also have a lot to do with that as well.
Precisely. Just because Russia allows 12 year olds at their Senior Nationals does not mean every country does or should.