Isn’t the processor like 2 years old tech by now?
No, the Xeon family of processors is easily 15 years old, but the ones that are going into the iMac Pro are the yet to be released Intel Xeon Gold series which replace their E5 and E7 Xeons. Apple's specs show that the Xeons that will be populating the iMac Pro will using 2666MHz ECC RAM and have Turbo Boost to 4.5GHz. there are only one series that meets those criteria that have the specs, the Xeon Gold 3.2GHz 8 Core and Xeon Gold 3.0GHz 18 core. Nothing else in Intel's Xeon listing matches those specs. These will be release by Intel sometime in the next month or two.
There is a higher level of Xeon processor called the Xeon Platinum, but the speed is no higher, just the number of cores. The Platinum line starts with 20 cores and goes up from there. Some of those can set you back over $60,000 per unit.
The 18 core Xeon that the Xeon Gold being used in the top of the line iMac Pro is replacing sells for $10,800 on discount from NewEgg. Intel has yet to establish retail prices for the soon to be released Gold and Platinum Xeons.