In my current file on Emerald, my Sceptile is level 68, but my Rayquaza is level 75. I don't think that counts, though, seeing as Rayquaza gets a 65-level head-start over your starter.
In Yellow, though, my Butterfree is level 95. I should get it to 100 one of these days. I beat pretty much the whole game with it, just like many players seem to do for the first gym or so, because Pikachu sucks in that regard. I just said, "Screw it," and left Pikachu in the box. To this day, my Pikachu is only at level 20. I've never even tried to evolve it, even before I found out online that it can't be evolved.