Your take: Is 2 years enough to learn the python programming language?
my take:
I think the language grows with time. There was python 2, now there is python 3. In the future, there probably will be python 4. So 2 years is not enough.
Your take:...................
1 year should be enough - your editor will alert you to most of the Python version differences.
If you are already a programmer you could learn Python in just one week or two following the official tutorial https://docs.python.org/3/tutorial/
If you are not a programmer you may be minimally proficient in about 2 years depending on how much hours you program per day, you need real world experience to learn.
Don't worry about the Python's version because the syntax is almost the same and the official libraries too, the differences are very little. There will be not a v4, maybe 10 years from now, and it will be still mostly compatible with v3.