The most memorable instance of overleveling when I was a kid was my Raichu in Ruby, which was somewhere in the 80s when I started the League challenge. If memory serves, there was less extreme overleveling with my Venusaur and Poliwrath in my first Leafgreen run, my Sceptile and Raichu in my first Emerald run, and EVERYTHING in the Johto games (seriously, the bosses are piss-weak in those games). I try to keep everything more or less balanced nowadays - my Pokemon might not all be at the same level, but the highest is within 5 levels of the lowest (I don't keep HM slaves on the main team anymore, only using them long enough to clear obstacles and then boxing them again). If I have a Sceptile, Galvantula, or Torterra, it MUST be the highest-leveled Pokemon on my story-mode team, though.