I don't think those dates are comparable. The Chinese program actually started in the 90s. https://en.wikipedia.org/wiki/J-XX
They have simply catched up. It's the same thing with the economy. In nominal terms, they were nowhere near top 3 only 15 years ago. Economic power -> military power, it's very simple. China has the largest economy in the world by PPP and the second largest military budget. It makes perfect sense.
Still, a few years to one way or another... that doesn't matter too much. But it's clear that both T-50 and J-20 will enter service around the same timeframe. J-20 seems to be ready (of course, without the final engines, but at this stage PAK-FA is no different) and in higher numbers, because China has more funding.
Also, one thing that Russia-bashers don't seem to get is that these potential "delays" are not a huge deal. Russia was always planning to acquire around 200-250 PAK-FAs, right? And that by mid-2030s? So who cares if they have 12 instead of 50+ by 2020? Order 12-16 aircraft per year on average after 2020 and you'll have more 200 in 20 years. It was never going to be Russia's F-35.