How long does each part last?

Part's all have a technically unlimited life-span. HDD's and PSU's will be the first failing parts, HDD most likely being the first.

Overall though, in general use most parts have 3-5years before things start to go weird. However, this is assuming very little cleaning and etc is done. Everything is electrical with no moving parts, as such in an ideal situation they are built to never fail.

To answer your specific question, a year old PSU is fine, but generally try to stay away from used parts (if thats what you mean?), on the graphics card end as long as it was kept well, there should be no concerns at all. For reference, my build is 3 years old, my build before that my friend uses, is 6 years old, and he still plays all the new games on it, all he did was upgrade the Video Card