The talk says that "10,000 hours" is, to within an order of magnitude, the amount of practice required to get expert-level performance: e.g. to be a professional athlete.
It says that, conversely, with a bit of practice you can get really good, really quickly.
The following is, I think, an example of the truth of that:
Those who pass their driving test have had, on average, about 45 hours of professional training combined with 22 hours of private practice. Learners who prepare this way, with a combination of plenty of professional training and plenty of practice, do better in the test.
- Driving a car in traffic is (IMO) a reasonably complicated skill.
- Doing it well enough to pass the driver's license test is doing it reasonably well.
- This statement from the British Government is presumably based on plenty of experience (experiment).
The cited time (45 plus 22) is a bit higher than the "20 hours" you asked about; but it's very much the same order of magnitude (much closer to "20 hours" than to "10,000 hours").
Beware though that the above is a (one) specific example, not a proof of the general case: it's "a" skill, not "any" skill.
The TED talk does actually say "any":
... about any skill you can think of. Want to learn a language? Want to learn how to draw? Want to learn how to juggle flaming chainsaws? If you put 20 hours of focused, deliberate practice into that ting, you will be astounded.
I suspect it's also possible to come up with some counter-examples: for example, that nobody gets "really good" at writing chinese in anything like 20 hours.