My cat's stool is soft?

From how it sounds this matter may be temporary. 7 months old and still developing so the grass may have had some effect on stool consistency. If kitty is behaving normally aside from poo issues, there is probably nothing to worry about. Sorry for the pun but "This too shall pass." If you are still concerned call your local animal shelter or vets office for advice. They should be able to tell you if there is any danger over the phone. Call a few and get some experienced advice. Hope this helps.