The foundation is a key element of any home.  Foundations take the weight of the building and spread it evenly over the soil.  When considering a vintage home one must know the foundation!  Many homes built before 1880 had no specific foundation work.  They were built on mud sills placed on the ground then framing was attached directly to the mud sills.  One should expect to replace this "no foundation" foundation.  Homes built before 1910 had brick foundations with concrete being introduced around that time.

If the foundation is brick watch for signs of potential trouble: loose and powdery mortar, crumbling bricks, cracks in bricks (especially running diagonally across a brick).  Talk to your home inspector about any of these issues. 

If a concrete foundation look for cracks.  Large cracks or cracks that don't match indicate uneven settlement or ground movement.  Smaller  cracks or hairlines mean only minor settlement and could stay that way for years.  All cracks should be repaired.

This is not meant as an complete study of foundations, that is clearly beyond my expertise.  If one suspects trouble consult a foundation contractor and an engineer.