Tool/Release Date Questions

Some questions for the community:

1. Are kits released prior to say the year 2000 generally considered to subpar?
2. Where is the best place to research kit original/retool release dates?
3. How do I know the age of the actual unopened kit in my hands?  A kit may have been originally released in 1995, but the kit in my hands could be only a year or two old, right? 
4. How well do decals in unopened boxes age?  Does the glue/paper etc start deteriorating after say 10 years?

Thanks.