taste of life: in most citations this corresponds to the idea of getting an experience of a particular kind of life. Notice that in most cases the word life is postmodified, that is followed by a phrase which talks about what kind of life it is: life in the Premier division, life down under (i.e. in Australia), etc. Possible translations might involve the noun εμπειρία or the verb δοκιμάζω
taste for life: this is generally not postmodified. The sense is much more like όρεξη γαι ζωή
the rather strange citation a taste for life under the knife refers to a woman who had a series of cosmetic surgery operations. Do you think this appeared in a newspaper or in a clinical report?