Good points. There still has to be a statistical average to give us a typical value…somewhere between 1 year and 40 years?
I think we’d have to narrow “Career” down first. If we include “Burger flipper” as a career, which it is for some, then the answer would be pretty meaningless.
So let’s narrow it down to “Careers with a Bachelors or better”.
I also think you’d have to narrow it down after that to mean "Careers for a person with no desire to “Move up the ladder”.
That being the case I would say that the number is much smaller than the one you gave, maybe 5 or less.
Look at teaching for instance. You’ve basically “Hit the ceiling” the second you’ve taken the job. Every raise you get is based on how long you’ve been there assuming you don’t try to “Move up” by getting a further degree, move to principle or something else. At the same token even something as complex as engineering you can pretty quickly hit the ceiling, again assuming you don’t try to move into any “Upper level” engineering, management etc.
As you said in almost any carreer it’s pretty easy to avoid the ceiling and I think most people with careers actually hit the ceiling and then avoid it a couple times before they “Hit it” and stop.
So a teacher will get a degree and other credits and “Avoid the ceiling” of the minimal education. An engineer will move from “Glorified Draftsman” right out of college to doing real engineering and then move to project management then maybe an engineering management position and so on. The issue is that after every “Avoidance” it becomes harder to avoid the next ceiling.
So in soild basic terms I would say your typical job will hit the first ceiling in a range from 0-5 years. I would say those “First ceilings” are probably pretty easy to avoid and most people do it by default without much effort.
I also think many people “Actively” avoid these ceilings and only say they “Hit the ceiling” when nothing but either a serious career change or serious additional work will get them to the next level. Moving into another field, additional degrees etc. I think for most this doesn’t happen until later in most careers, probably 10-20 years.
All completely WAG’s…which is what I do best 
So in summary I think you have to look at it two ways.
1 - If a person with a degree gets a job, learns the job and nothing more when will they hit the point where they make no more money than the typical annual increase. IMO that comes quickly and for most jobs less than five years.
2- If a person with a degree gets a job, learns the job plus learns everything else they can about the company. Works to move up the “Company ladder” at what point will they hit the point at which the only way they can continue to move up is thru different methods than “On the job learning”, I would say that comes latter, 10-20 years or so.
The guy in the first scenario can “Move up” by simply putting forth a little more effort in many cases. The guy in the second scenario will have to either get another degree, change companies or possibly even careers to go any further.
FWIW the guy in the first scenario probably wouldn’t say he “Hit the ceiling”, likely because they really don’t care…which is why they’ve hit the ceiling. Only the persons in the second scenario would notice, because they’ve worked to get there.
~Matt