How old is too old?

[Chendra Grandhi]

I am looking at properties in San Antonio and Indy areas for now. Most of the multi unit or apartment/commercial properties are very old. Some good ones are 1900, 1920, etc. I am rarely seeing any thing newer than 1980. I am worried about buying in to a money pit, how old is too old according to you? What I should be prepared for in terms of maintenance and cap ex? 

I am planning to get inspections done at the minimum.