NoCode is right but something else to bear in mind is that, for this to work cleanly, all tracks on an album need to be tagged with the same year (or in the same decade). Otherwise the same album will appear in several decades. A solution to this would be to create a new field (Tools>Options>Tree & View Settings>Add) and put decade (80s, 90s etc) in there.
One advantage of this approach is that you can tag an album with a particular decade without necessarily knowing what year the tracks were released in. e.g. If you have a 'greatest hits of the 80s album' or a 'Howard Jones greatest hits album' etc you could just assign a decade of 80s without knowing the year for each track.
I used to use the grouping by year method but then realised that I was missing a lot of tracks in the relevant decade because the year wasn't tagged. These were therefore listed as 'Unassigned'. Now - every track in my library has a decade tag, though only about 75% have the year.