% steph@apexPDell2 (/home/stephan/t) %
% cat data.txt # I added the last line                                                                       

item  group  entry_date
34     gr1    2003-03-02
12     gr1    1990-03-14
39     gr3    2002-04-11
66     gr4    2006-03-16
32     gr3    1998-02-13
90     gr1    2004-06-15
55     gr4    1999-06-15
10     gr1    2003-03-02

% steph@apexPDell2 (/home/stephan/t) %
% LC_ALL=C sort -k 3 data.txt | perl -lna -e 'print if $F[1] eq q{gr1} and $F[0] == 34'
34     gr1    2003-03-02

% steph@apexPDell2 (/home/stephan/t) %
% sort -k 3 data.txt | grep gr1 | sort -n | head -n1
10     gr1    2003-03-02