Maybe your input data is not what you think it is? Instead of piping the data in try using an external file or baking the data into a test script:

use strict;
use warnings;

my %res;
while (<DATA>)
{
    chomp;
    my ( $name, $rest ) = split /\t/;
    push @{ $res{$name} }, $rest;
}
for $a( sort keys %res )
{
    print "$a:". join( "~~", @{ $res{$a} } );
    print "\n";
}

__DATA__
nick    5
nick    10
george    2
peter    3
george    14
nick    20
[download]

Prints:

george:2~~14
nick:5~~10~~20
peter:3
[download]

Note that that result is not what you say you want, but your code suggests the comma you show as a separator for george is a typo anyway.