Shimano 600
 

Where does the 600 group fit in the hierarchy? I can find it on the internet. But no real information about quality.

600 is what they used to call ultegra before they called it ultegra. It is at the same level as ultegra. I have an old crit bike that has 600 aned it still works great.

Any idea how old it might be?
I ask because i have a chance to buy a used Serotta with 600 components. I am still trying to figure out if it's a good deal or not.

I think they changed it to Ultegra in late 80s or very early 90s. You should be careful I think primarily for the free wheel, which will proabbyl be a free whell and not a cassette. It may be hard to get parts for it. ALso make sure about how the bottom bracket and headset is threaded and their diameter, again for parts availability issues. Otherwsie, 600 is a great gruppe and will work well.