name = haha
age  = 9 
sex  = male

 1 #!/usr/bin/perl
 2 use strict;
 3 use 5.010;
 4 use Tie::File;
 5 tie my @contents, 'Tie::File', './test_file' or die "can't open $!\n";
 6 for(@contents){
 7     s/(^age\s*=\s*)\d+/${1}90/;
 8 }
 9 untie @contents;
10 exit 0;

perl -pi -e 's/(^age\s*=\s*)\d/${1}90/' test_file

sed -i -n -e 's/\(^age *= *\)[0-9]\+/\190/' test_file