This is an incredibly cornball idea, completely worthless for any naturally rational mind, which sounds like it was designed to help out irrational game-obsessed apes instead.

As an irrational game-obsessed ape, I wholeheartedly approve. Thumbs up.

I think a single common leveling scale isn't a useful idea. For instance, I'm not a salesman, and in the other popular context of "cold approaches", doing them would probably reduce the level of my marriage! A scale for each of a few dozen skills would be interesting, though.

Unless this sort of game becomes unbelievably popular, you could try to find some way to calibrate levels by percentiles. Someone in the bottom tenth percentile of (local? national? first-world? age-adjusted!) skill would be level 0, someone in the 97th through 98.5th percentile might be level 20, etc.