i haven’t posted this response since I swore off reddit for a bit — but thought this might be interesting to other folks.
Let’s take a step back. I find it really dangerous to assume there’s a causal link or 1:1 correlation between [people who spend all their time studying a field] and [people who are extremely competent at a field].
For one, this leads to a culture of “all work, all the time.” For instance, professors are expected to work essentially all the time by default. Another example: In programming, there’s this growing trend of using contributions (often unpaid) to open-source projects as a benchmark for competency.
This becomes problematic when, for various reasons, people cannot devote their spare time to the study of a field. Maybe it is financial: they don’t have time to spare to make unpaid contributions to OSS. Maybe it is life-related: a small child or family is taking up a lot of their spare time.
The overly-simplistic thinking you outlined leads to people in positions of power / employers discriminating against or manipulating young women in the field because they might get pregnant and have less spare time to study the field for a while (there are other issues at play here, for instance maternal / significant other leave, and the expectation that women do most of the child-rearing work). Another possible result is systematic exclusion of lower-income people from the field, because they can afford less unpaid work relative to high-income people.
Secondly, I think it’s absolutely true that people (whether for nurture, e.g. previous exposure, learning styles, presence of mentors, presence with curricula that matches their learning style, enjoying studying instead of thinking about family members getting shot up, etc. or nature) will pick up a new field at different rates. Thus, it is definitely possible for motivated people new to a field to catch up very fast with people who have been studying the field for a while (not to mention bringing in fresh perspectives and new ideas). I don’t know any names off the top of my head, but I can look around for examples if you would like. 
This could, fortunately or unfortunately, mean there exists
- an extremely intelligent and motivated 9 to 5 brogrammer who has officially been in the field for 10 years
who is as technically competent as
- someone who toils night and day and has been officially in the field for 30 years
Whether this actually happens, or if so the frequency with which it happens, I have no idea.
Therefore, I find it much less problematic to assume something along the lines of
- “people who enjoy a field so much they would study it in their spare time if they could, or who study it whenever possible, tend to be the ones who persevere and become extremely competent at it”
- “only people who study the field in their spare time are extremely competent at it”.
 I apologize for the bad syntax. I meant 10x, not O(n). I think my brain went “abbreviate Order of magNitude” and shat out O(n). I find it no more rude than correcting usage of “I could care less” or “should of”, which some people may find rude, but which I tend to appreciate.
 Perhaps Einstein is an example of someone who caught up in a field rapidly without officially studying it full time, although now I feel obligated to pull up examples of non-dead-white-men, since someone on the Internet will make the wrong conclusion otherwise.
Sadly, so far in my life most of my curriculum has given me biopsies of white male geniuses, so I can’t say for sure as I don’t know the life history of many non-white-male people (also, I don’t know the life histories of many not-famous people).
Technical people I could try to vet to see whether they could be considered “examples”:
- Non-male: Emmy Noether, Marie Curie, Dr. Grace Murray Hopper, Hedy Lamarr, Émilie du Châtelet, Laura Deming (living). (thanks quora). Sufiah Yusof , Kathleen Holtz
- Non-white: Srinivasa Ramanujan, Kim Ung-Yong (still living), Akrit Jaswal (err… reportedly not at all humble), Jaylen Bledsoe (living)
- Non-male non-white (black): Rochelle Ballantyne (living), Brittney Exline (living)
 (now that was sad to read about, but happy update: http://inquiringfeminist.com/2015/02/13/neil-tweedie-of-the-daily-telegraph/)