Only Adobe could know, and there is no chance they would reveal such commercially sensitive information. And what would you mean by average: licenses or revenue? Mean, mode or median? Total or per contributor? Adobe's income or contributor income? In what country and currency? Etc
For this, I would try to contact Adobe directly instead of using this mostly user to user forum with some Adobe participation. I never looked into Adobe's earning reports, but if there is public information available, it will be in those earning reports.
ABAMBO | Hard- and Software Engineer | Photographer