When you have constant prints like this

print "\nHere is a list to select from:\n";
print "A. Set input filename\n";
...
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It could be better writen with here documents:

print END;
This is
text that
only needs one print
END
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There were so many places where you made an error, I thought I'd like to point this out: good job on using <STDIN> instead of <>.

chomp ( $selec = <STDIN> );
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Where you use this:

$selec =~ s/[a-z]/[A-Z]/;
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The substitution could be better written:

$selec =~ tr/a-z/A-Z/;
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and that could be better written without a regex:

$selec = uc($selec);
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Where you have the switch like statement:

if ( $selec eq 'A' ) {
        namefile();
        Menu ();
        }
...
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You might want to look into something like this:

%func = (A => \&namefile, B=> \&openfile, ...)
...
$func{$selec}->();
Menu();
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Here, you could do better to add a 'my'

my ( $last, $first, $age, $sex, $height, $weight, $comment ) = split (
+/,/);
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Also, you might want to look into having a data structure somewhat like this:

$age[$i++] ={last=>$last,first=>$first,age=>$age,sex=>$sex,height=>$he
+ight,weight=>$weight,comment=>$comment}
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And you would use it like this:

print "First last=$age[0]{last}\n";
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Also, if you change the datastructure, you might want to look into a Shwartzian Transfer.

Sorry for the briefness on some topics, but there were a lot : ) If you still have questions, just ask.

The 15 year old, freshman programmer,
Stephen Rawls