I would argue that it
isn't, because it simply pushes the boundary back, and possibly making it even less appropriate.
I can't see having valid or "compelling" research experience as an undergraduate while taking a full load of classes (ok, so you have to take advanced placement courses in high school, which my school did not offer even if my school district did; I'm not sure one way or the other about that) and possibly working to support yourself (I'll leave the alternatives as an exercise to the reader).
At this point, you're filtering on many criteria that have absolutely nothing to do with successful research.