If they are well stored then I wouldn’t expect the older vintages to be past peak at all. Well stored Barolo from the '50s and '60s drink extremely well. One item to be aware of is that during that time period of '90s through mid 2000s there was a big modernist movement with a lot of new French oak and rotofermenters and short macerations, all of which was designed to make plush, approachable wines, but the end result was not very representative of the region and I’d be skeptical of how some have held up. There is still some of this kind of thing, but it is much less. So my advice is before buying, do some research on producers. Searching here on WB should be sufficient. The linked thread is a good place to start.
If you have questions about specific bottles or producers which you are considering, I am sure many here would be able to offer opinions.