I find it hard to believe the tires in the pics above have travelled 21,000 mi. They look barely used. As discussed, the date shown in the second picture is not the official manufacturers date stamp.
Tire discussion threads are only second to oil discussion threads in terms of opinions. So much depends on your climate, the environment (where geographically) and how the bike/tires are stored (environment), and the kind of riding and roads you ride on. It also depends on your risk tolerance.
For me, I bought a bike a few years ago with original 2009 tires that had travelled only 3,000 mi. They looked brand new with no signs of wear or aging. I chose to keep them on and use them. Remember that our Canadian climate is cooler than many places in N.A. and this bike was/is always stored indoors, and not near any electrical equipment (ozone), windows (UV) etc.
Just this Spring when I was doing my pre-season inspection, I noticed some very fine spider-webbing appeared inside the tread groves for the first time. The side walls showed no signs of aging or weather checking and the beads looked fine. I've kept a close eye on these tires this season and just last weekend decided to swap them out after travelling 10,000 miles.
The side walls and inside carcasses were like new still. The tread wear indicators showed they were due for a swap out and the spider webbing progressed from a very fine status to slightly larger but nothing major.
So, I guess I'm the contrarian here and of the opinion that regarding tires, it just depends. BTW - I just changed out my 3/4 ton truck's Michelin LTX M&S tires after only 40,000 mi. It is an occasional driver and not used for work. The truck is parked outside and these tires are exposed to the weather 24/7/365.
The truck's tires were 8 years old (rotated annually with snow tires) yet still had 7/16th tread left. For the most part, they looked great. However, I observed some non-standard weather checking in the sidewalls of all four tires and decided they were not worth the risk to continue driving with even on an occasional, non-loaded basis.
So for me, it's all about risk management, knowing your equipment and staying on top of things like regular inspections, tire maintenance, (pressures, balancing, rotations & alignments etc.) Like I said above, it just depends. To each their own.
DDX, if you have ANY doubt about their road worthiness, change them out and you will at least sleep better.