Ok, quick down and dirty solution here, in case you can't wait... :)
Download the attached adopt.php and then replace the one on your site with the attached file.
The attached file by default will make it so a user cannot have more than 4 pets with levels less than 6. To change these values, open the file in wordpad or another text editor and change:
PHP Code:
$query = "SELECT * FROM owned_adoptables WHERE currentlevel < '6' and owner='".$username."'";
Change the number 6 here to the level where adoptables must be to be considered adult and do not count against the user's total.
Change the number 4 here to be the maximum number of young adoptables a user can have before the system denies them new pets. :)
I haven't tested this file but it should work. Let me know how it works. :)
Brandon