I need population and age breakdown data for Detroit. I have found census tract shapefiles but none with the attribute data that I need.
Any idea where I might find such data?
To answer your question in general, Shapefiles from the US Census Bureau do not come prepopulated with any of the Census Tables. See https://www.census.gov/geo/education/howtos.html for guides on how to link the tract shapefiles (geography) with Census tables. In particular, Downloading Data from American FactFinder to use with TIGER/Line Shapefiles [PDF] or Joining Census Data to TIGER/Line Shapefiles [PDF]
However as others have pointed out, this data may also be found in ready to use format from a city GIS website. Check out Data Driven Detroit: https://datadrivendetroit.org. They have several sets of Demographic Data, such as listed on this page: http://portal.datadrivendetroit.org/datasets/?group_id=25cbacb151854daba75685f6f1a4a7f2&q=demographic&sort_by=relevance