HOWEVER, if the evolutionist is arguing the relative merits of their respective views with a creationist, the fact that the oldest fish is older than the oldest man does NOT in any way support his position over against the creationist position-unless that person has stated that he is a young earth creationist.
Since this is the only example you offered, I will comment on it:
This is not the argument that science makes. It is a comic book version of it creationists adore to address in place of the real argument, since that gives the impression that 13th century modes of pure logical reasoning are an adequate approach to understanding (and disregarding) scientific theories.
The strength of the scientific argument does not rest on the unadorned notion that fish is older than folks; it rests on an enormous web of independently derived evidence of morphological, geological, and paleo-microbiological co-ordinated continuity of evidence, that fish fossels form a tiny set of data points within.
And of course I didn't say it did. This was presented as a very simple example of a case where evolutionist and creationist approaches predict the same things in data. It is a common rhetorical device to construct a simple case on which both sides can agree and then use it as a springboard to address more complex questions.
If evolutionary advocates so quickly jump to all kinds of conclusions not inherent in the discussion at hand, no progress is ever made in the discussions.