I'd say that it isn't too late, but it's really up to you
I agree with BitcoinboyBlog. You'd want to start with a huge capital in order to really make good money off Bitcoin mining. It isn't too late as many would have said.
Where do you get that 2/3 are already mined? Agree also that thos is not late to build your own mining sites, mining of bitcoin is always profitable it only depeneding on the hardware did you used. Much better to buy high class antminer to make your income much stable and quick Return of investment. Do not hesitate to do what do you want some of the advise is negative and there is also a positive reply but all of this is up to you mate just follow what your heart beats goodluck mate hope your decision would be successful.