The confusion comes from a bad fit between your [level of measurement][1] and UI element. You should tailor elements to the data. 

Years are usually counted with integers, so a timeline is an appropriate representation for them. But in choosing hard, preselected intervals, you have done what is called ["binning" the data][2]. After binning, you are left with just a few categories of data. But the timeline still looks like the timelines we all know, which are for single year numbers. 

If you are really just interested if a construction year falls into one of these bins, look into methods for representing categorical data. Choose one of those, and order them chronologically, reflecting the fact that they are not in fact categorical, but ordinal. This will give you data which is rather easy to work with, but not as precise. The radio buttons from the upvoted answers are a very good solution. If you don't want to use them for some reason, you can probably make some control with similar functionality which looks different, maybe breaking up the timeline into very distinct intervals and making only one selectable at a time. 

The slider as shown fits the idea of choosing a specific year. I


  [1]: http://en.wikipedia.org/wiki/Level_of_measurement
  [2]: http://en.wikipedia.org/wiki/Data_binning