I figured out that characters with adventuring classes are close to 0.005% of the population, using the percentage of professional athletes in North America to set the numbers.
Low levels (less than 4) might be ten times as common, but high levels (above 10) are likely ten times as rare. The population of a region is 0.0005% level 10+ adventurers, with wizards in specific being a tenth that.
In a fantasy world (we'll go with the Realms, since we have numbers) there could be 50 to 75 million people on a continent. In the Realms, there'd be 34,000 adventurers, with over 30k being rookies while 3,400 are "professional". But only 34 wizards in the 10-20 range across Faerûn. A couple per major region or one per nation.
That'd be the guy you'd have to tap to remove the laugh lines from your face. It's like going to the Surgeon General for a face lift. They can do it, and if you throw enough money at them they'll probably say "yes", but since they're spending a full 8-hour work day on the task it's going to be expensive.