Most dry cleaners can remove old stains on clothing but it depends on how old the stain is and how deep the stain is ingrained into the clothes.
The longer a stain sits and dries the harder the stain is to remove from the clothing.
However if the clothing stain has only been in the clothing for a few months or so then the dry cleaner may be able to remove the stain using some commercial clothing stain remover.
Dry cleaners have access to more powerful yet safe stain removal chemicals that can usually remove most stains.
But even some harder to remove stains can be impossible or at least near impossible even for a good dry cleaning company to get out.
The dryer cleaner should be able to tell you if your stain should be able to be removed but they cannot really guarantee it.
I've had good luck with some old stains being removed by dry cleaners and then a few older stains were near impossible to remove but they got some of it out.