Two words with the same meaning: eski and yaşlı. Is there difference in when to use which or can I pick one at random?

´Eski´ is generally used fto describe old things or times (in the ´old days´ and ´yaşlı´ to describe people.

 Thanks LIR.

An addition:

"yaşlı" to describe animals and all kind of living things as well. For example "yaşlı bir kedi" (an old cat), "yaşlı bir ağaç" (an old tree).

 Oh yes!  I was actually originally going to say ´yaşlı´ is for animate objects and ´eski´ for inanimate objects!