The LGA775 platform is a dead platform. Intel already made cheaper models for it and after that stopped because the new platforms 1156 and 1366 arrived. Trying to sell the new chips and chip sets, Intel decided to not drop prices on the old tech meaning the stores or intermediary companies did not drop their prices also and the stock of the older chips was halted as well because the price/performance ratio was better with the new arrivals.
If you want to find out how old is the CPU just ask Google or Intel. All chips have a release date. If you want to know exactly how old the chip is you can find that info written on the chip(if i remember right).
Yes, the chip might have been heavily overclocked or stressed and it might fail soon, but that's not always the case.
Yes the issue with any Socket 775 processor is that they are discontinued and we haven't made any new ones in a couple years. So depending on the processor that you are looking for it may have been discontinued for 2 to 4 years ago.
The real issue with used processors has to deal with how they were handled by the person before you. We talk about that little old lady and her car but with her computer she may have never cleaned out the dust from the computer that the chip was in so processor may have been running hot for years.
I know some people that have a old Intel® Pentium 3 processor that they are still doing email and other junk off from. These systems are over 12 years old. The simple truth is that a other things in a computer will go bad before the processor unless you were really facing heating issues. So odds are that you wouldnt see an issue with a processor wearing out under normal wear and tear but you want to make sure that you can return the processor if you get a bad one.
Actually one of those people was me about 3 years ago i was working off two pentium 3 laptops.
I just dug them out to possibly sell, they work but they are really beat up as they have been around the world with me. but they were not used every day and often parked for months at a time when i was at home.
an ibm a31
an ibm t21
for what its worth I have heard Intel chips go bad less then AMD chips.